Gemstones: Malachite

Malachite cultivated
Malachite cultivated
Malachite cultivated
Malachite untreated
Malachite untreated
Malachite untreated

Malachite — a talisman for children.

Color: Malachite is an opaque, banded stone, the colors in the bands range from a very light green to almost deep green.

Description: Cu2CO3(OH)2 , Malachite is a semi-precious stone and also a valuable copper ore, hydrous copper carbonate. It is responsible for the green color of tarnished copper and bronze. Because of its distinctive bright green color and its presence in the weathered zone of nearly all copper deposits, malachite serves as a prospecting guide for that metal. Malachite has been used as an ornamental stone and as a gemstone.

The name’s origin: Malachite derives its name from Greek word malakos – soft. According to another theory the word malachite comes from Greek malhe, which means grass.

Wedding anniversary: Malachite is the anniversary gemstone for the 13th year of marriage.

Care and treatment: Malachite is especially fragile. Protect malachite from scratches and sharp blows. Also avoid large temperature changes. Do not clean malachite in a home ultrasonic cleaner. Washing malachite in water will remove its protective polish. If setting or repairing in jewelry be careful of heat since a jeweler’s torch can damage the stone.

From the stone history: Mining Malachite began as early as 4000 BC by ancient Egyptians. In the Middle ages, malachite was worn to protect from black magic and sorcery. In Ancient Greece amulets for children were made of malachite.
In the New Stone Age came the discovery of the possibility of extracting certain metals from the ores in which they generally occur. Probably the first such material to be used was malachite, then already in use as a cosmetic and easily reduced to copper in a strong fire. It is impossible to be precise about the time and place of this discovery, but its consequences were tremendous. Namely it led to the search for other metallic ores, to the development of metallurgy.

Shopping guide: Malachite is a beautiful green earth stone with irregular black banding. It is easily recognized by its color, green streak, and silky or velvety lustre. It is beautiful in earrings, necklaces, and pendants. Imitation malachite has very regular black or white banding.

Healing ability: Malachite is said to aid in the regeneration of body cells, creates calm and peace, and aids one’s sleep.

Mystical power: A gorgeous stone, Malachite is worn by many to detect impending danger. This beautiful green stone offers bands of varying hues and is believed by many to lend extra energy. It is believed that gazing at Malachite or holding it relaxes the nervous system and calms stormy emotions. Malachite is said to bring harmony into one’s life. It is also believed that malachite gives knowledge and patience. Malachite is used as a children’s talisman to ward off danger and illness. It is attached to infant’s cradles.

Deposits: The most important mine is in Zaire. Notable occurrences are in Ural, Siberia, France, South Australia, Namibia and USA (Arizona).

Posted by Ajitchandra vijayji at  7:37 AM 0 comments



SodaliteSodalite is named in reference to the sodium content it has. It is found in light to dark pure blue color and is well known in the semi-precious stone world. It is the only feldspathoid which contains chlorine.

Sodalite balances the mental and emotional bodies. It cleanses the aura, soothes and calms inflammations. It fuels a person’s creative processes and also enhances wisdom. It helps to make clear and rational decisions. It builds self confidence, helps fight lymphatic cancer and also boost the immune system.

Sodalite is found in Namibia, Brazil, Canada and the USA. The hardness is 6 and specific gravity, 2.13 – 2.29.

Lapis Lazuli

Gemstones: Lapis Lazuli

Lapis Lazuli
Lapis Lazuli
Lapis Lazuli
Lapis Lazuli
Lapis Lazuli round plate
Lapis Lazuli
Statuette of goat made of Lapis Lazuli

Lapis Lazuli is a gemstone compared to stars in the sky.

Stone’s names: Lapis Lazuli, Lazurite.

Color: Lapis Lazuli occurs in various shades of blue with some qualities being speckled with white calcite and some with yellow pyrite. The finest Lapis Lazuli is even blue color with little or no veining from other elements.

Description: Lapis lazuli is a semiprecious stone valued for its deep blue color. The source of the pigment ultramarine, Lapis lazuli is not a mineral but a rock colored by lazurite. In addition to the sodalite minerals in lapis lazuli, small amounts of white calcite and of pyrite crystals are usually present.
Because lapis is a rock of varying composition, its physical properties are variable.

The name’s origin: The name lapis comes from word pencil in Spanish.

Wedding anniversary: Lapis Lazuli is the anniversary gemstone for the 7th and 9th year of marriage.

Care and treatment: Lapis Lazuli can easily be scratched or chipped. Water can dissolve the stone’s protective coatings, hence clean your lapis lazuli jewelry with a soft dry cloth.

From the stone history: Lapis Lazuli with deep azure blue color, often flecked with golden pyriteinclusions, was treasured by ancient Babylonian and Egyptian civilizations and often worn by royalty. Lapis lazuli was widely used by Egyptians for cosmetics and painting . Persian legend says that the heavens owed their blue color to a massive slab of Lapis upon which the earth rested. Lapis Lazuli was believed to be a sacred stone, buried with the dead to protect and guide them in the afterlife.
Lapis lazili is one of the gemstones, that used incommesso, also called florentine mosaic. Commesso is a technique of fashioning pictures with thin, cut-to-shape pieces of brightly colored, semiprecious stones, developed in Florence in the late 16th century. The stones most commonly used are agatesquartzes,chalcedonies,jaspers, granites, porphyries, petrified woods, and lapis lazuli. Commesso pictures, used mainly for tabletops and small wall panels, range from emblematic and floral subjects to landscapes.
Visit – the online store that offer a large collection of pictures decorated with natural precious and semiprecious stones.
For centuries Lapis Lazuli has been prized for jewelry. But it has also been used to make the beautiful blue paint ultramarine and has been used as a source of writing instruments. Ultramarine is used in paints, lacquers, and decorating materials. It has a particularly brilliant blue color and is very lightfast.

Shopping guide: Lapis lazuli has been widely used as a semiprecious stone throughout history. It is most often seen as a necklace of beads or carved pendants.
Fine natural Lapis Lazuli can be rather pricey. Jewelry with the high quality stones with no calcite or pyriteveins can be quite expensive. Much of the jewelry that is sold as Lapis is an artificially colored jasper from Germany that shows colorless specks of clear, crystallized quartz and never the goldlike flecks of pyrite.

Healing ability: The stone is said to increase psychic abilities. Lapis is said to be a cure for melancholy and for certain types of fever. Lapis lazuli eliminates negative emotions. It relieves sore throat pain.

Mystical power: Traditionally believed to increase mental clarity, virility, and calm. Lapis Lazuli is energy focuser for teachers, lecturers and speakers. Enhances creative self-expression. It is believed to be useful in relieving depression and promoting spirituality. Lapis Lazuli is also powerful during meditation.

Deposits: The main supplies of Lapis Lazuli are found in the Afghanistan, Egypt, Canada, Chile, the US, and South America. The most important sources are the mines in Badakhshan, northeastern Afghanistan, and near Ovalle, Chile, where gemstone is usually pale rather than deep blue.



Dumortierite from Madagascar

Dumortierite is a fibrous variably colored aluminium boro-silicate mineral, Al6.5-7BO3(SiO4)3(O,OH)3. Dumortierite crystallizes in theorthorhombic system typically forming fibrous aggregates of slender prismatic crystals. The crystals are vitreous and vary in color from brown, blue, and green to more rare violet and pink. Substitution of iron and other tri-valent elements for aluminium result in the color variations. It has a Mohs hardness of 7 and aspecific gravity of 3.3 to 3.4. Crystals show pleochroism from red to blue to violet.Dumortierite quartz is blue colored quartz containing abundant dumortierite inclusions.

Dumortierite was first described in 1881 for an occurrence in Chaponost, in the Rhône-Alps ofFrance and named for the Frenchpaleontologist Eugene Dumortier (1803-1873). It typically occurs in high temperature aluminium rich regional metamorphic rocks, those resulting fromcontact metamorphism and also in boron rich pegmatites. The most extensive investigation on dumortierite was done on samples from the high grade metamorphic Gfohl unit in Austria by Fuchs et al. (2005).

It is used in the manufacture of high grade porcelain. It is sometimes mistaken for sodalite and has been used as imitation lapis lazuli.

Sources of Dumortierite include AustriaCanadaFranceItalyMadagascarNamibia,NevadaNorwayPolandRussia and Sri Lanka

Posted by Ajitchandra vijayji at  1:29 AM 0 comments




Benitoite on natrolite
Category Silicate mineral
Chemical formula BaTiSi3O9
Color Blue; Colorless
Crystal habit Tabular dipyramidal crystals, granular
Crystal system Hexagonal
Cleavage [1011] Poor
Fracture Conchoidal
Mohs Scalehardness 6 – 6.5
Luster Vitreous
Streak White
Diaphaneity Transparent to translucent
Specific gravity 3.6
Refractive index 1.757-1.759; 1.802-1.804
Pleochroism Dichroic (blue to white)
Solubility Insoluble: HClH2SO4
Soluble: HF
References [1][2]

Benitoite is a rare blue barium titanium silicate mineral, found in hydrothermally alteredserpentinite. Benitoite fluoresces under short wave ultraviolet light, appearing light blue in color.

It was first described in 1907 by George D. Louderback, who named it benitoite, “as it occurs near the head waters of the San Benito River in San Benito County,” California.[3][4]

Uses of benitoite

Benitoite’s main uses are as collector’s specimens, especially in specimens which show off this mineral’s unique crystals, or specimens in which benitoite occurs with its commonly associated minerals. Benitoite’s hardness also makes it suitable for use as a gemstone, though the general lack of usable material has limited this use.

Associated minerals and locations

Benitoite typically occurs with an unusual set of minerals, along with minerals that make up its host rock. Frequently associated minerals include:

natrolite Na2Al2Si3O10 · 2H2O
neptunite KNa2Li(FeMn)2Ti2Si8O24
joaquinite NaBa2FeCe2(TiNb)2(SiO3)8(OHF) · 1H2O
serpentine (MgFe)3Si2O5(OH)4
albite NaAlSi3O8

Blue Benitoite Crystals on white natrolite, Dallas Gem Mine, San Benito Co., California, USA

Benitoite is a rare mineral found in very few locations including San Benito County, California,Japan and Arkansas. In the San Benito occurrence it is found in natrolite veins withinglaucophane schist within a serpentinite body. In Japan it occurs in a magnesio-riebeckite-quartz-phlogopite-albite dike cutting a serpentinite body.[5] Benitoite is typically found with some combination of natrolite, joaquinite, and neptunite on a greenish-grey serpentinite base.

Benitoite is the official state gem of California.




Prehnite, Epidote
Category Silicate mineral
Chemical formula Ca2Al(AlSi3O10)(OH)2
Color Colorless to gray to yellow, yellow-green or white
Crystal habit Globular, reniform to stalactitic
Crystal system Orthorhombic – Pyramidal
Cleavage Distinct on [001]
Fracture Brittle
Mohs Scalehardness 6 – 6.5
Luster Vitreous – pearly
Specific gravity 2.8 – 2.95
Optical properties Biaxial (+)
Refractive index nα = 1.611 – 1.632 nβ = 1.615 – 1.642 nγ = 1.632 – 1.665
Birefringence δ = 0.021 – 0.033
References [1][2][3]

Prehnite is a phyllosilicate of calcium and aluminium with the formula: Ca2Al(AlSi3O10)(OH)2. Limited Fe3+ substitutes for aluminium in the structure. Prehnite crystallizes in theorthorhombic crystal system. It is brittle with an uneven fracture and a vitreous to pearly lustre. Its hardness is 6-6.5, its specific gravity is 2.80-2.90 and its color varies from light green to blue or white. It is translucent.

Though not a zeolite, it is found associated with them and with datolitecalcite, etc. in veins and cavities of basaltic rocks, sometimes in granitessyenites, or gneisses. It is an indicator mineral of the prehnite-pumpellyite metamorphic facies. It was first described in 1789 for an occurrence in Haslach, Harzburg and Oberstein, Germany, and named for Colonel Hendrik Von Prehn (1733-1785), an early Dutch governor of the Cape of Good Hope colony.[1]



Category Magnesium mineralsCalcium mineralsSilicate minerals
Chemical formula MgCaSi2O6
Color Green
Crystal habit Short prismatic crystals common, may be granular[1]
Crystal system Monoclinic[2]
Twinning Simple and multiple twins common on {100} and {001}[1]
Cleavage Distinct/good on {110}[2]
Fracture Irregular/uneven, conchoidal[2]
Tenacity Brittle[2]
Mohs Scalehardness 5½ – 6½[2]
Luster Vitreous to dull[2]
Streak white[2]
Density 3.278 g/cm3[2]
Refractive index nα= 1.663 – 1.699, nβ= 1.671 – 1.705, nγ= 1.693 – 1.728[2]
Birefringence δ = 0.030[2]
Dispersion Weak to distinct, r>v [2]

Diopside is a monoclinic pyroxene mineral with composition MgCaSi2O6. It forms complete solid solution series with hedenbergite(FeCaSi2O6) and augite, and partial solid solutions withorthopyroxene and pigeonite. It forms variably colored, but typically dull green crystals in themonoclinic prismatic class. It has two distinct prismatic cleavages at 87 and 93° typical of the pyroxene series. It has a Mohs hardness of six, a Vickers hardness of 7.7 GPa at a load of 0.98 N[3], and a specific gravity of 3.25 to 3.55. It is transparent to translucent with indices of refraction of nα=1.663–1.699, nβ=1.671–1.705, and nγ=1.693–1.728. The optic angle is 58° to 63°.

Diopside is found in ultramafic (kimberlite and peridotiteigneous rocks, and diopside-rich augite is common in mafic rocks, such as olivine basalt and andesite. Diopside is also found in a variety of metamorphic rocks, such as in contact metamorphosed skarnsdeveloped from high silica dolomites. It is an important mineral in the Earth‘s mantle and is common inperidotite xenoliths erupted inkimberlite and alkali basalt.

Diopside is a precursor of chrysotile (white asbestos) by hydrothermal alteration and magmatic differentiation;[4] it can react with hydrous solutions of magnesium and chlorine to yield chrysotile by heating at 600°C for three days.[5] Some vermiculite deposits, most notably those in Libby, Montana, are contaminated with chrysotile (as well as other forms of asbestos) that formed from diopside.[6]

At relatively high temperatures, there is a miscibility gap between diopside and pigeonite, and at lower temperatures, between diopside and orthopyroxene. Thecalcium/(calcium+magnesium+iron) ratio in diopside that formed with one of these other two pyroxenes is particularly sensitive to temperature above 900°C, and compositions of diopside in peridotite xenoliths have been important in reconstructions of temperatures in the Earth’s mantle.

Gemstone quality diopside is found in two forms: the black star diopside and the chrome diopside (which includes chromium giving it a rich green colour). At 5.5–6.5 on the Mohs scale, chrome diopside is relatively soft to scratch. Mohs scale of hardness does not measure tensile strength or resistance to fracture.

Violane is a manganese rich variety of diopside, violet to light blue in colour.[7]

Chrome diopside ((Ca,Na,Mg,Fe,Cr)2(Si,Al)2O6) is a common constituent of peridotitexenoliths, and dispersed grains are found nearkimberlite pipes, and as such are a prospecting indicator for diamonds. Occurrences are reported in Canada, South Africa, Russia and a wide variety of other locations.

Diopside was first described about 1800 and derives its name from the Greek dis, “twise”, andòpsè, “face” in reference to the two ways of orienting the vertical prism.



Category Mineral
Chemical formula (Li,Na)AlPO4(F,OH)
Color Generally white or creamy, but can also be colorless or pale yellow, green, blue, beige, gray, brown or pink.
Crystal habit Prismatic to columnar form
Crystal system Triclinic
Twinning Microscopic polysynthetic twinning common
Cleavage [100] Perfect, [110] Good, [011] Distinct
Fracture Irregular/Uneven,Sub-Conchoidal
Mohs Scalehardness 5.5 – 6[1]
Luster Vitreous to pearly[1]
Specific gravity 2.98 – 3.11
Polish luster greasy to vitreous (in gem material)[1]
Optical properties Double refractive, biaxial, may be either positive or negative[1]
Refractive index na=1.577 – 1.591,
nb=1.592 – 1.605,
nc=1.596 – 1.613
Birefringence .020 – .027[1]
Pleochroism weak to none[1]
Ultravioletfluorescence very weak green in long wave, light blue phosphorescence in long wave and short wave [1]

Amblygonite is a fluorophosphate mineral, (Li,Na)AlPO4(F,OH), composed of lithium,sodiumaluminiumphosphatefluoride andhydroxide. The mineral occurs in pegmatitedeposits and is easily mistaken for albite and other feldspars. Its density, cleavage and flame test for lithium are diagnostic. Amblygonite forms a series with montebrasite, the low fluorine endmember. Geologic occurrence is in granite pegmatites, high-temperature tin veins, andgreisens. Amblygonite occurs with spodumeneapatite,lepidolitetourmaline, and other lithium-bearing minerals in pegmatite veins. It contains about 10% lithium, and has been utilized as a source of lithium. The chief commercial sources have historically been the deposits of California and France.


The mineral was first discovered in Saxony by August Breithaupt in 1817, and named by him from the Greek amblus, blunt, andgouia, angle, because of the obtuse angle between the cleavages. Later it was found at Montebras, Creuse, France, and at Hebron inMaine; and because of slight differences in optical character and chemical composition the names montebrasite and hebronite have been applied to the mineral from these localities. It has been discovered in considerable quantity at Pala in San Diego county,California; Caceres, Spain; and the Black Hills of South Dakota. The largest documented single crystal of amblygonite measured 7.62×2.44×1.83 m3 and weighed ~102 tons.[2]


Transparent amblygonite has been faceted and used as a gemstone. As a gemstone set into jewelry it is vulnerable to breakage and abrasion from general wear, as its hardness and toughness are poor.[1] The main sources for gem material are Brazil and the U.S..Australia,FranceGermanyNamibiaNorway, and Spain have also produced gem quality amblygonite.[1]




Dioptase from Altyn Tübe, Kazakhstan, thetype locality
Category Mineral
Chemical formula Copper silicate hydrate: CuSiO3·H2O
Color Dark blue green, emerald green
Crystal habit Six sided prisms terminated by rhombohedrons to massive
Crystal system Trigonal; bar 3
Cleavage Perfect in three directions
Fracture Conchoidal and brittle
Mohs Scalehardness 5
Luster Vitreous
Streak Green
Specific gravity 3.28–3.35
Refractive index 1.65–1.71

Dioptase is an intense emerald-green to bluish-green copper cyclosilicate mineral. It is transparent to translucent. Itsluster is vitreous to sub-adamantine. Its formula is CuSiO3·H2O (also reported as CuSiO2(OH)2). It has a hardness of 5, the same as tooth enamel. It specific gravity is 3..28–3.35, and it has two perfect and one very good cleavage directions. Additionally, dioptase is very fragile and specimens must be handled with great care. It is atrigonal mineral, forming 6-sidedcrystals that are terminated by rhombohedra.


Late in the 18th century, copper miners at the Altyn-Tyube (Altyn-Tube) mine, Karagandy Province,Kazakhstan [1] thought they found an emerald deposit of their dreams. They found fantastic cavities in quartz veins in a limestone, filled with thousands of lustrous emerald-green transparent crystals. The crystals were dispatched to MoscowRussia for analysis. However the mineral’s inferior hardness of 5 compared with emerald’s greater hardness of 8 easily distinguished it. Later Fr.René Just Haüy (the famed French mineralogist) in 1797 determined that the enigmatic Altyn-Tyube mineral was new to science and named it dioptase (Greek,dia, “through” and optima, “vision”), alluding to the mineral’s two cleavage directions that are visible inside unbroken crystals.


Dioptase from the Tsumeb Mine, TsumebNamibia

Dioptase is a very rare mineral found mostly in desert regions where it forms as a secondary mineral in the oxidized zone of copper sulfide mineral deposits. However, the process of its formation is not simple, the oxidation of copper sulfides should be insufficient to crystallize dioptase as silica is normally minutely soluble in water except at highly alkaline pH. The oxidation of sulfides will generate highly acidic fluids rich in sulfuric acid that should suppress silica solubility. However, in dry climates and with enough time, especially in areas of a mineral deposit where acids are buffered by carbonate, minute quantities of silica may react with dissolved copper forming dioptase and chrysocolla.

The Altyn Tube mine in Kazakhstan still provides handsome specimens; a brownish quartzite host distinguishes its specimens from other localities. The finest specimens of all were found at the Tsumeb Mine in TsumebNamibia. Tsumeb dioptase is wonderfully lustrous and transparent, with its crystal often perched on an attractive snow-white carbonate matrix. Dioptase is also found in the deserts of the southwestern USA. A notable occurrence is the old Mammoth-Saint Anthony Mine near Mammoth, Arizona where small crystals that make fine micromount specimens are found. In addition, many small, pale-green colored crystals of dioptase have come from the Christmas Mine near Hayden, Arizona. Another classic locality for fine specimens is Renéville, Congo-Brazzaville. Finally, an interesting occurrence is the Malpaso Quarry in Argentina. Here tiny bluish-green dioptase is found on and in quartz. It appears at this occurrence, dioptase is primary and has crystallized with quartz, native copper, and malachite.

Dioptase crystals fromDemocratic Republic of the Congo, displaying the dioptasecrystal habit of six sidedprisms terminated byrhombohedrons


Dioptase is popular with mineral collectors and it is occasionally cut into small emerald-likegems. Dioptase and chrysocollaare the only relatively common copper silicate minerals. A dioptase gemstone should never be exposed to ultrasoniccleaning or the fragile gem will shatter.



Category Minerals
Chemical formula Al2SiO5
(aluminium silicate)
Color Blue; also green, white, grey, black
Crystal habit Columnar; fibrous; bladed
Crystal system Triclinic
Cleavage [100] Perfect, [010] Imperfect
Fracture Brittle
Mohs Scalehardness 4.5-5 parallel to one axis
6.5-7 perpendicular to that axis
Luster Vitreous; Pearly
Streak White
Diaphaneity Transparent to translucent
Specific gravity 3.56 – 3.67
Refractive index 1.71 – 1.75
Pleochroism Trichroic, colorless to pale blue to blue
Solubility None
Phase diagram of the Aluminosilicates.[1]

Kyanite from Brazil

Kyanite, whose name derives from the Greek word kyanos, meaning blue, is a typically blue silicate mineral, commonly found in aluminium-rich metamorphic pegmatites and/orsedimentary rock. Kyanite inmetamorphic rocks generally indicates pressures higher than 4 kilobars. Although potentially stable at lower pressure and low temperature, the activity of water is usually high enough under such conditions that it is replaced by hydrous aluminosilicates such asmuscovitepyrophyllite, or kaolinite.

Kyanite is a member of the aluminosilicate series, which also includes the polymorphandalusite and the polymorphsillimanite. Kyanite is strongly anisotropic, in that its hardnessvaries depending on its crystallographic direction. While this is a feature of almost all minerals, in kyanite this anisotropism can be considered an identifying characteristic.

At temperatures above 1100 °C, kyanite decomposes into mullite and vitreous silica via the following reaction: 3(Al2O3·SiO2) → 3Al2O3·2SiO2 + SiO2. This transformation results in an expansion.[2]

Uses of kyanite

Kyanite is used primarily in refractory and ceramic products, including porcelain plumbing fixtures and dishware. It is also used in electrical insulators and abrasives. Kyanite has been used as a gemstone, though this use is limited by its anisotropism and perfect cleavage. Kyanite is one of the index minerals that are used to estimate the temperature, depth, and pressure at which a rock undergoes metamorphism. Finally, as with most minerals, kyanite is a collector’s mineral.

Associated minerals

Kyanite is usually found in association with its polymorphs, as well as other silicate minerals. These include:

Alternative names

Kyanite has several alternative names, including disthene, munkrudite and cyanite. White-grey kyanite is also called rhaeticite.

Notes for identification

Kyanite’s elongated, columnar crystals are usually a good first indication of the mineral, as well as its color (when the specimen is blue). Associated minerals are useful as well, especially the presence of the polymorphs or staurolite, which occur frequently with kyanite. However, the most useful characteristic in identifying kyanite is its anisotropism. If one suspects a specimen to be kyanite, verifying that it has two distinctly different hardnesses on perpendicular axes is a key to identification.



Category Phosphate mineral
Chemical formula AlPO4·2H2O
Color Green, blue green, yellow green and rarely red
Crystal habit Encrustations and reniform masses
Crystal system Orthorhombic – dipyramidal
Cleavage [010] perfect
Fracture Conchoidal to splintery
Mohs Scalehardness 4.5
Luster Vitreous to waxy
Streak White
Diaphaneity Transparent to translucent
Specific gravity 2.57 to 2.61
Optical properties Biaxial (-)
Refractive index nα = 1.563 nβ = 1.588 nγ = 1.594
Birefringence δ = 0.031
References [1][2][3]

Cut slab of Variscite at theSmithsonian. Specimen is roughly 0.5 m wide.

Variscite is a hydrated aluminium phosphate mineral (AlPO4·2H2O). It is a relatively rare phosphate mineral. It is sometimes confused with turquoise; however, variscite is usually greener in color.

Variscite is a secondary mineral formed by direct deposition from phosphate-bearing water that has reacted with aluminium-rich rocks in a near-surface environment. It occurs as fine-grained masses in nodules, cavity fillings, and crusts. Variscite often contains white veins of the calcium aluminium phosphate mineral crandallite.

Variscite is sometimes used as a semi-precious stone, and is popular for carvings and ornamental use. It was first described in 1837 and named for the type locality of Variscia, the historical name of Vogtland in Germany. At one time, variscite was called Utahlite. At times, materials which may be turquoise or may be variscite have been marketed as “variquoise”. Appreciation of the color ranges typically found in variscite have made it a popular gem in recent years.[4]

Variscite from Nevada typically contains black spiderwebbing in the matrix and is often confused with green turquoise. Most of the Nevada variscite recovered in recent decades has come from mines located in Lander County.[5]

Notable localities are Lucin, Utah and Fairfield, Utah in the United States. It is also found inGermanyAustraliaPolandSpain[6] andBrazil.




Fluorite crystals on display at the Cullen Hall of Gems and Minerals
Category mineral
Chemical formula calcium fluoride CaF2
Color Colorless, white, purple, blue, blue-green, green, yellow, brownish-yellow, pink or red
Crystal habit Occurs as well-formed coarse sized crystals also massive – granular
Crystal system IsometriccF12, SpaceGroup Fm-3m, No. 225
Cleavage Octahedral…or…[111] Perfect, [111] Perfect, [111] Perfect.
Fracture Uneven
Mohs Scalehardness 4
Luster Vitreous
Streak White
Specific gravity 3.18
Refractive index 1.433–1.435
Fusibility 3
Solubility Slightly in water
Other characteristics sometimesphosphoresceswhen heated or scratched. Other varietiesfluoresce

Fluorite (also called fluorspar) is a halide mineral composed of calcium fluorideCaF2. It is an isometricmineral with a cubic habit, though octahedral and more complex isometric forms are not uncommon. Cubic crystals up to 20 cm across have been found at Dalnegorsk, Russia.[1] Crystal twinning is common and adds complexity to the observed crystal habits.

The word fluorite is derived from the Latin root fluo, meaning “to flow” because the mineral has a relatively low melting point and was used as an important flux in smelting. Fluorite gave its name to its constitutive element fluorine.


Fluorite may occur as a vein deposit, especially with metallic minerals, where it often forms a part of thegangue (the worthless “host-rock” in which valuable minerals occur) and may be associated with galena,sphaleritebaritequartz, and calcite. It is a common mineral in deposits of hydrothermal origin and has been noted as a primary mineral in granites and other igneous rocks and as a common minor constituent ofdolostone and limestone.

Fluorite is a widely occurring mineral which is found in large deposits in many areas. Notable deposits occur in GermanyAustria,SwitzerlandEnglandNorwayMexico, and Ontario in Canada. Large deposits also occur in Kenya in the Kerio Valley area within the Great Rift Valley. In the United States, deposits are found in MissouriOklahomaIllinoisKentuckyColoradoNew Mexico,ArizonaOhioNew Hampshire,New YorkAlaska and Texas.. Flourite has been the state mineral of Illinois since 1965. At that time, Illinois was the largest producer of fluorite in the United States; however, the last Illinois mine closed in 1995.

The largest documented single crystal of fluorite was a cube 2.12 m in size and weighed ~16 tons.[2]

Blue John

Vein of Blue John in Treak Cliff Cavern

One of the most famous of the older-known localities of fluorite is Castleton in DerbyshireEngland, where, under the name ofDerbyshire Blue John, purple-blue fluorite was extracted from several mines/caves, including the famous Blue John Cavern.. During the 19th century, this attractive fluorite was mined for its ornamental value. The name derives from French “bleu et jaune” (blue and yellow) characterising its color. Blue John is now scarce, and only a few hundred kilograms are mined each year for ornamental andlapidary use. Mining still takes place in the nearby Treak Cliff Cavern.

Recently discovered deposits in China have produced fluorite with coloring and banding similar to the classic Blue John stone.[citation needed]


Many samples of fluorite fluoresce under ultra-violet light, a property that takes its name from fluorite[3]. Many minerals, as well as other substances, fluoresce. Fluorescence involves the elevation of electron energy levels by quanta of ultra-violet light, followed by the progressive falling back of the electrons into their previous energy state, releasing quanta of visible light in the process. In fluorite, the visible light emitted is most commonly blue, but red, purple, yellow, green and white also occur. The fluorescence of fluorite may be due to impurities such as yttrium or organic matter in the crystal lattice. It is not surprising, therefore, that the color of visible light emitted when a sample of fluorite is fluorescing appears dependent on where the original specimen was collected, different impurities having been included in the crystal lattice in different places. Neither does all fluorite fluoresce equally brightly, even from the same locality. Thereforeultra-violet light is not a reliable tool for the identification of specimens, nor for quantifying the mineral in mixtures. For example, among British fluorites, those from NorthumberlandCounty Durham, and EasternCumbria are the most consistently fluorescent, whereas fluorite from YorkshireDerbyshire, and Cornwall, if they fluoresce at all, are generally only feebly fluorescent.

Fluorite also exhibits the property of thermoluminescence.


Fluorite comes in a wide range of colors and has subsequently been dubbed “the most colorful mineral in the world”. The most common colors are purple, blue, green, yellow, or clear. Less common are pink, red, white, brown, black, and nearly every shade in between. Color zoning or banding is commonly present. The color of the fluorite is determined by factors including impurities, exposure to radiation, and the size of the color centers.


There are three principal types of industrial use for fluorite, corresponding to different grades of purity. Metallurgical grade fluorite, the lowest of the three grades, has traditionally been used as a flux to lower the melting point of raw materials in steel production to aid the removal of impurities, and later in the production of aluminium. Ceramic (intermediate) grade fluorite is used in the manufacture ofopalescent glassenamelsand cooking utensils. The highest grade, acid grade fluorite, is used to make hydrofluoric acid by decomposing the fluorite with sulfuric acid. Hydrofluoric acid is the primary feedstock for the manufacture of virtually all organic and inorganic fluorine-containing compounds, including fluoropolymers andperfluorocarbons, and is also used to etch glass.

Fluorite is used instead of glass in some high performance telescopes and camera lens elements. Exposure tools for thesemiconductor industry make use of fluorite optical elements for ultraviolet light at 157 nm wavelength. Fluorite has a uniquely high transparency at this wavelength. Fluorite has a very lowdispersion so lenses made from it exhibit less chromatic aberration than those made of ordinary glass. In telescopes it allows crisp images of astronomical objects even at high power. Fluorite also has ornamental and lapidary uses.. Canon Inc. produces synthetic fluorite crystals that are used in their more expensivetelephoto lenses.Nikon has previously manufactured at least one all-fluorite element camera lens (105 mm f/4.5 UV) for the production of ultraviolet images.

Fluorite objective lenses are manufactured by the larger microscope firms (Nikon, OlympusCarl Zeiss and Leica) due to their strong hexagonal crystal structure most notable for evenly refracting light. Their transparence to ultraviolet light enables them to be used forfluorescence microscopy. The fluorite also serves to correct optical aberrations in these lenses.


Fluorite (yellow), calcite (white/grey) and pyrite (gold specs), El Hammon Mine, Morocco

Yellow fluorite (~ 4 cm in height)

Deep purple cubes of fluorite with galena (gray) and calcite (white) from Illinois, USA

Pig carved in fluorite, 5 cm (2 inches) long

Mineral fluorite

Octahedral fluorite crystals from New Mexico, USA

Cleaved fluorite octahedra

The unit cell of fluorite’s crystal structure

Fluorite with Iron Pyrite and Calcite blooms




Chrysocolla from Nevada, USA
Category Silicate mineral
Chemical formula (Cu,Al)2H2Si2O5(OH)4·nH2O
Color Blue, blue-green, green
Crystal habit Massive, nodular, botryoidal
Crystal system Orthorhombic
Cleavage none
Fracture Brittle to sectile
Mohs Scalehardness 2.5 – 3.5
Luster Vitreous to dull
Streak white to a blue-green color
Diaphaneity Translucent to opaque
Specific gravity 1.9 – 2.4
Optical properties Uniaxial (+)
Refractive index nω = 1.460 nε = 1.570
Birefringence +0.110

Chrysocolla (hydrated copper silicate) is a mineral, (Cu,Al)2H2Si2O5(OH)4·nH2O. It is of secondary origin and forms in the oxidation zones of copper ore bodies. Associated minerals are quartzlimoniteazuritemalachitecuprite, and other secondary copper minerals.

Chrysocolla has an attractive blue-green colour and is a minor ore of copper, having ahardness of 2.5 to 3.5. It is also used as an ornamental stone. It is typically found as glassybotryoidal or rounded masses and crusts, or vein fillings. Because of its light color, it is sometimes confused with turquoise. Commonly it occurs only as pourous crusts unsuitable for gem use, but high quality, gem grade chrysocolla can be translucent and is highly prized.



The name comes from the Greek chrysos, “gold”, and kolla, “glue”, in allusion to the name of the material used to solder gold, and was first used by Theophrastus in 315 BCE.

Notable occurrences include IsraelDemocratic Republic of CongoChileCornwall inEngland, and ArizonaUtahNew Mexico and Pennsylvania in the United States.




Sample of cerussite-bearing quartzite
Category Carbonate mineral
Chemical formula Lead carbonate: PbCO3
Color Colorless, white, gray, blue, or green
Crystal habit Massive granular, reticulate, tabular to equant crystals
Crystal system Orthorhombic – Dipyramidal (2/m 2/m 2/m)
Twinning Simple or cyclic contact twins
Cleavage Good [110] and [021]
Fracture Brittle conchoidal
Mohs Scalehardness 3 to 3.5
Luster Adamantine, vitreous, resinous
Streak White
Diaphaneity Transparent to translucent
Specific gravity 6.53 – 6.57
Optical properties Biaxial (-)
Refractive index nα = 1..803 nβ = 2.074 nγ = 2.076
Birefringence δ = 0.273
Other characteristics May fluoresce yellow under LW UV
References [1][2]

Cerussite (also known as lead carbonate or white lead ore) is a mineral consisting of leadcarbonate (PbCO3), and an importantore of lead. The name is from the Latin cerussa, white lead. Cerussa nativa was mentioned by Conrad Gessner in 1565, and in 1832F. S. Beudantapplied the name cruse to the mineral, whilst the present form, cerussite, is due to W. Haidinger (1845). Miners’ names in early use were lead-spar and white-lead-ore.

Cerussite crystallizes in the orthorhombic system and is isomorphous with aragonite. Like aragonite it is very frequently twinned, the compound crystals being pseudo-hexagonal in form. Three crystals are usually twinned together on two faces of the prism, producing six-rayed stellate groups with the individual crystals intercrossing at angles of nearly 60°. Crystals are of frequent occurrence and they usually have very bright and smooth faces. The mineral also occurs in compact granular masses, and sometimes in fibrous forms. The mineral is usually colorless or white, sometimes grey or greenish in tint and varies from transparent to translucent with an adamantine lustre. It is very brittle, and has a conchoidal fracture. It has aMohs hardness of 3 to 3.75 and a specific gravity of 6.5. A variety containing 7 % of zinc carbonate, replacing lead carbonate, is known as iglesiasite, from Iglesias in Sardinia, where it is found.

The mineral may be readily recognized by its characteristic twinning, in conjunction with the adamantine lustre and high specific gravity. It dissolves with effervescence in dilute nitric acid. A blowpipe test will cause it to fuse very readily, and gives indications for lead.

As crystaline ore

Finely crystallized specimens have been obtained from the Friedrichssegen mine in Lahnsteinnear NassauJohanngeorgenstadt inSaxonyMies in BohemiaPhoenixville in Pennsylvania,Broken Hill, New South Wales; and several other localities. Delicate acicular crystals of considerable length were found long ago in the Pentire Glaze mine near St Minver in Cornwall. It is often found in considerable quantities, and contains as much as 77.5% of lead.

Lead(II) carbonate is practically insoluble in neutral water (solubility product [Pb2+][CO32-] ≈ 1.5×10-13 at 25 °C), but will dissolve in dilute acids.

Commercial uses

White lead” is the key ingredient in (now discontinued) lead paints. Ingestion of lead-based paint chips is the most common cause of lead poisoning in children.[3]

Both “white lead” and lead acetate have been used in cosmetics throughout history, though this practice has ceased in Western countries.[4]



For other uses, see Serpentine (disambiguation).


The serpentine group describes a group of common rock-forming hydrous magnesium ironphyllosilicate ((Mg,Fe)3Si2O5(OH)4minerals; they may contain minor amounts of other elements including chromiummanganesecobalt andnickel. In mineralogy and gemology, serpentine may refer to any of 20 varieties belonging to the serpentine group. Owing to admixture, these varieties are not always easy to individualize, and distinctions are not usually made. There are three important mineral polymorphs of serpentine: antigoritechrysotile andlizardite.


“Their olive green color and smooth or scaly appearance is the basis of the name from the Latin serpentinus, meaning serpent rock,” according to Best (2003). They have their origins inmetamorphic alterations of peridotite and pyroxene. Serpentines may also pseudomorphouslyreplace other magnesium silicates. Alterations may be incomplete, causing physical properties of serpentines to vary widely. Where they form a significant part of the land surface, the soil is unusually high in clay.

Antigorite is the polymorph of serpentine that most commonly forms during metamorphism of wet ultramafic rocks and is stable at the highest temperatures—to over 600°C at depths of 60 km or so. In contrast, lizardite and chrysotile typically form near the Earth’s surface and break down at relatively low temperatures, probably well below 400°C. It has been suggested that chrysotile is never stable relative to either of the other two serpentine polymorphs.

Samples of the oceanic crust and uppermost mantle from ocean basins document thatultramafic rocks there commonly contain abundant serpentine. Antigorite contains water in its structure, about 13 percent by weight. Hence, antigorite may play an important role in the transport of water into the earth in subduction zones and in the subsequent release of water to create magmas in island arcs, and some of the water may be carried to yet greater depths.

Soils derived from serpentine are toxic to many plants, because of high levels of nickel,chromium, and cobalt; growth of many plants is also inhibited by low levels of potassium andphosphorus and a low ratio of calcium/magnesium. The flora is generally very distinctive, with specialised, slow-growing species. Areas of serpentine-derived soil will show as strips ofshrubland and open, scattered small trees (often conifers) within otherwise forested areas; these areas are calledserpentine barrens.

Most serpentines are opaque to translucent, light (specific gravity between 2.2–2.9), soft (hardness 2.5–4), infusible and susceptible to acids. All are microcrystalline and massive inhabit, never being found as single crystalsLuster may be vitreous, greasy or silky. Colours range from white to grey, yellow to green, and brown to black, and are often splotchy or veined. Many are intergrown with other minerals, such as calcite and dolomite. Occurrence is worldwide; New Caledonia,Canada (Quebec), USA (northern California), Afghanistan,CornwallChinaAsiaFranceNorway and Italy are notable localities.

Rock composed primarily of these minerals is called serpentinite. Serpentines find use in industry for a number of purposes, such as railway ballasts, building materials, and the asbestiform types find use as thermal and electrical insulation (chrysotile asbestos). The asbestos content can be released to the air when serpentine is excavated and if it is used as a road surface, forming a long term health hazard by breathing. Asbestos from serpentine can also appear at low levels in water supplies through normal weathering processes, but there is as yet no identified health hazard associated with use or ingestion. In its natural state, some forms of serpentine react with carbon dioxide and re-release oxygen into the atmosphere.

The more attractive and durable varieties (all of antigorite) are termed “noble” or “precious” serpentine and are used extensively as gems and in ornamental carvings. Often dyed, they may imitate jade. Misleading synonyms for this material include “Korean jade”, “Suzhou jade”, “Styrian jade”, and “New jade”. New Caledonian serpentine is particularly rich in nickel, and is the source of most of the world’s nickel ore.

Polished slab of bowenite serpentine, a variety of antigorite. Typical cloudy patches and veining are apparent.

The Māori of New Zealand once carved beautiful objects from local serpentine, which they called tangiwai, meaning “tears”. Material quarried in Afghanistan, known as sang-i-yashm, has been used for generations. It is easily carved, taking a good polish, and is said to have a pleasingly greasy feel.

The lapis atracius of the Romans, now known as verde antique, or verde antico, is a serpentinite breccia popular as a decorative facing stone. In classical times it was mined atCasambalaThessalyGreece. Serpentinite marbles are also widely used: GreenConnemara marble (or Irish green marble) from ConnemaraIreland (and many other sources), and redRosso di Levanto marble from Italy. Use is limited to indoor settings as serpentinites do not weather well.


Lamellated antigorite occurs in tough, pleated masses. It is usually dark green in color, but may also be yellowish, gray, brown or black. It has a hardness of 3.5–4 and its luster is greasy. The monoclinic crystals show micaceous cleavage and fuse with difficulty. Antigorite is named after its type locality, the Valle di Antigorio in Italy.

Bowenite is an especially hard serpentine (5.5) of a light to dark apple green color, often mottled with cloudy white patches and darker veining. It is the serpentine most frequently encountered in carving and jewellery. The name retinalite is sometimes applied to yellow bowenite. The New Zealand material is called tangiwai.

Although not an official species, bowenite is the state mineral of Rhode Island: this is also the variety’s type locality. A bowenite cabochon featured as part of the “Our Mineral Heritage Brooch”, was presented to First Lady Mrs. Lady Bird Johnson in 1967.

Williamsite is a local varietal name for antigorite that is oil-green with black crystals ofchromite or magnetite often included. Somewhat resembling fine jade, williamsite is cut into cabochons and beads. It is found mainly in Maryland andPennsylvaniaUSA.[1]


Polished serpentine, from theVal d’Aosta, sold asGressoney. Used at theUnited Nations building in New York.

Extremely fine-grained, scaly lizardite (also called orthoantigorite) comprises much of the serpentine present in serpentine marbles. It is triclinic, has one direction of perfect cleavage, and may be white, yellow or green. Lizardite is translucent, soft (hardness 2.5) and has an average specific gravity of 2.57. It can be pseudomorphous after enstatite,olivine or pyroxene, in which case the name bastite is sometimes applied. Bastite may have a silky lustre.

Lizardite is named after its type locality on the Lizard PeninsulaCornwallUK.[2] It is worked by local artisans into various trinkets which are sold to tourists.

The California State Rock is Serpentinite.



A fragment of ulexite displaying characteristic optical property

Ulexite from California

Ulexite (NaCaB5O9·8H2O) (hydrated sodium calcium borate hydroxide) is a mineral occurring in silky white rounded crystalline masses or in parallel fibers. It was named after the German chemist Georg Ludwig Ulex (1811−1883) who first discovered it.

Ulexite is a structurally complex mineral, with a basic structure containing chains of sodium, water and hydroxide octahedra. The chains are linked together by calcium, water, hydroxide and oxygen polyhedra and massive boron units. The boron units have a formula of B5O6(OH)6and a charge of -3, and are composed of three borate tetrahedra and two borate triangular groups. Hardness is 2 (softer than a fingernail) and specific gravity is approximately 1.97.[1]

Ulexite is found with the mineral borax and is directly deposited in arid regions from the evaporation of water in intermittent lakes called playas. The precipitated ulexite commonly forms a “cotton ball” tuft of acicular crystals. Ulexite is also found in a vein-like bedding habit composed of closely-packed fibrous crystals, also known as “TV rock” or “TV stone” due to its unusual optical characteristics. The fibers of TV rock act as fiber optics, transmitting light along their lengths by internal reflection, and when a piece of TV rock is cut with flat polished faces perpendicular to the orientation of the fibers a good-quality specimen will display an image of whatever surface is adjacent to its other side (as shown in the photograph).

Ulexite from California

The fiber-optic effect is the result of the polarization of light into slow and fast rays within each fiber, the internal reflection of the slow ray, and the refraction of the fast ray into the slow ray of an adjacent fiber. An interesting consequence is the generation of three cones, two of which are polarized, when a laser beam obliquely illuminates the fibers. These cones can be seen when viewing a light source through the mineral.[1]

Ulexite decomposes in hot water. It is found principally in California and Nevada, USA;Tarapaca Region in Chile, and Kazakhstan.



Category Silicate mineral
Chemical formula Ca2B5SiO9(OH)5
Color White to colorless
Crystal habit Massive to nodular, occurs as tabular prisms flattened parallel to [100]
Crystal system Monoclinic
Cleavage absent
Fracture conchoidal, uneven
Mohs Scalehardness 3.5
Luster vitreous to dull
Streak white
Diaphaneity Translucent
Specific gravity 2.53 – 2.59
Optical properties Biaxial (-) 2V = 73°
Refractive index nα = 1.583 – 1.586 nβ = 1.596 – 1.598 nγ = 1.600
References [1][2][3]

Howlite, a calcium borosilicate hydroxide (Ca2B5SiO9(OH)5), is a silicate mineral found inevaporite deposites.[4] Howlite was discovered at Tick Canyon, California in 1868 by Henry How (1828 – 1879), a Canadian chemist, geologist, and mineralogist.[1][3]

In appearance, it is white with fine grey or black veins in an erratic, often web-like pattern, and is opaque with a sub-vitreous lustre. Its structure is monoclinic with a Mohs hardness of 3.5 and lacks regular cleavage.

Howlite, dyed blue as a turquoise simulant

Howlite is commonly used to make decorative objects such as small carvings or jewelry components. Because of its porous texture, howlite can be easily dyed to imitate other minerals, especially turquoise because of the superficial similarity of the veining patterns. The dyed howlite (or magnesite) is marketed as turquenite.[5] Howlite is also sold in its natural state, sometimes under the misleading trade names of “white turquoise” or “white buffalo turquoise”, or the derived name “white buffalo stone”.



This article is about the mineral. For other uses, see Onyx (disambiguation).

Onyx is a cryptocrystalline form of quartz. The colors of its bands range from white to almost every color (save some shades, such as purple or blue). Commonly, specimens of onyx available contain bands of colors of white, tan, and brown.Sardonyx is a variant in which the colored bands are sard (shades of red) rather than black. Pure black onyx is common, and perhaps the most famous variety, but not as common as onyx with banded colors.

Sardonyx (banded agate). The specimen is 2.5 cm (1 inch) wide.

It is usually cut as a cabochon, or into beads, and is also used for intaglios and cameos, where the bands make the image contrast with the ground. Some onyx is natural but much is produced by the staining of agate.

The name has sometimes been used, incorrectly, to label other banded lapidary materials, such as banded calcite found inMexicoPakistan, and other places, and often carved, polished and sold. This material is much softer than true onyx, and much more readily available. The majority of carved items sold as ‘onyx’ today are this carbonate material.[1]

Technical details
Chemical composition and name SiO2Silicon dioxide
Hardness (Mohs scale) 7
Specific gravity 2.65 – 2.667
Refractive index (R.I.) 1.543 – 1.552 to 1.545 – 1.554
Birefringence 0.009
Optic sign Positive
Optical character Uniaxial


Onyx comes through Latin from the Greek onyx meaning ‘claw’ or ‘fingernail’. With its fleshtone color, onyx can be said to resemble a fingernail. The English word ‘nail’ is cognatewith the Greek word.[2]

Historical usage

Onyx from Australia.

Onyx from Brazil.

The Beinecke Rare Book and Manuscript Library at Yale University was originally planned to be coated in green onyx. However, there wasn’t sufficient green onyx in the world to build such a structure, so that the designers used marble. Onyx was known to the ancient Greeks and Romans.[3] Use of sardonyx appears in the art of Minoan Crete, notably from the archaeological recoveries at Knossos.[4] Onyx was used in Egypt as early as the Second Dynasty to make bowls and other pottery items.[5] It is also mentioned in Exodus 25.

Black onyx with bands of colors.



Not to be confused with tuff, a hard volcanic rock that is sometimes called tufa.

Tufa towers at Mono LakeCalifornia.

Tufa forming the Trona Pinnacles, California.

This article is about the geological formation. For the historic Chinese name, see Southern Liang.

Tufa (sometimes also known as sinter) is a soft, friable and porous calcite rock. It is acalcium carbonate (CaCO3) deposit that forms by chemical/biological precipitation from bodies of water with a high dissolved calcium content. Calcareous tufa is not to be confused with tuff, a hard volcanic rock that is also sometimes called tufa.

Tufa deposition occurs in seven known ways:

  1. Mechanical precipitation by wave action against the shore. This form of tufa can be useful for identifying the shoreline of extinct lakes (for example in the Lake Lahontanregion).
  2. Precipitation from supersaturated hot spring water entering cooler lake water.
  3. Precipitation in lake bottom sediments which are fed by hot springs from below.
  4. Precipitation from calcium-bearing spring water flowing into an alkaline lake.
  5. Precipitation throughout a lake as the lake water evaporates, leaving the lake supersaturated in calcium.
  6. Through the agency of algaeMicrobial influence is often vital to tufa precipitation and may be involved in the other methods listed.
  7. Precipitation from cold water springs (for example in the foothills of the Rocky Mountains near Hinton, Alberta).

Tufa is common in many parts of the world. There are some prominent towers of tufa at Mono Lake and Trona Pinnacles in California, USA, formed by the fourth method mentioned above whilst submerged and subsequently exposed by falling water levels. Tufa is also common inArmenia and Great Britain.

Practical use

Tufa is today occasionally shaped into a planter. Its porous consistency makes tufa ideal foralpine gardens. A concrete mixture called hypertufa is used for similar purposes.

Orbicular jasper

Orbicular jasper

Orbicular jasper from Madagascar

Orbicular jasper is a variety of jasper which contains variably-colored orbs or spherical inclusions or zones. In highly silicifiedrhyolite or tuffquartz and feldspar crystallize in radial aggregates of needle-like crystals which provide the basis or seed for the orbicular structure seen in this kind of jasper[1]. The material is quite attractive when polished and is used as an ornamental stone orgemstone.

Various local or commercial names have been used for the material, such as kinradite, oregonite, owyhee jasper, ocean jasper and poppy-patterned jasper, depending on the source.Poppy-patterned jasper or Poppy jasper is the varietal name for material fromMorgan Hill,Santa Clara County, California. The trade name ocean jasper is used for a variety found along the intertidal shores of northeast Madagascar. In Nebraska orbicular jasper is found in altered rhyolite beds noted for a variety of jaspers and related agates.



For other uses, see Alabaster (disambiguation).

An uplighter lamp made from Italian alabaster (white and brown types). The base is 5 inches (13 cm) in diameter

Alabaster vase of Tutankhamun

Alabaster is a name applied to varieties of two distinct mineralsgypsum (a hydrous sulfate ofcalcium) and calcite (a carbonate of calcium). The former is the alabaster of the present day; the latter is generally the alabaster of the ancients.

The two kinds are readily distinguished from one another by their relative hardness. The gypsum kind is so soft as to be readily scratched by a fingernail (Mohs hardness 1.5 to 2), while the calcite kind is too hard to be scratched in this way (Mohs hardness 3), though it does yield readily to a knife. Moreover, the calcite alabaster, being a carbonateeffervesces on being touched withhydrochloric acid, whereas the gypsum alabaster, when so treated, remains practically unaffected.

Due to the characteristic color of white alabaster, the term has entered the vernacular as ametonym for white things, particularly “alabaster skin”. The usage as whiteness also occurs in a line from the poem and song, America the Beautiful.


The origin of alabaster is in Middle English, through Old French alabastre, in turn derived fromLatin alabaster and that from Greekαλάβαστρος (alabastros) or αλάβαστος (alabastos), the latter being the word for a vase made of alabaster.[1] This may further derive from the ancient Egyptian word a-labaste (vessel of the Egyptian goddess Bast).[2][3] It has been suggested that the name was derived from the town of Alabastron in Egypt, while an Arabic etymological origin has also been suggested.[4]


Calcite alabaster

This substance, the “alabaster” of the Bible, is often termed Oriental alabaster, since the early examples came from the Far East. The Greek name alabastrites is said to be derived from the town of Alabastron, in Egypt, where the stone was quarried, but the locality probably owed its name to the mineral; the origin of the mineral name is obscure. This “Oriental” alabaster was highly esteemed for making small perfume bottles or ointment vases called alabastra, and this has been conjectured to be a possible source of the name. Alabaster was also employed in Egypt for canopic jars and various other sacred and sepulchral objects. A splendidsarcophagus, sculptured in a single block of translucent calcite alabaster from Alabastron, is in the Sir John Soane’s MuseumLondon. This was discovered by Giovanni Belzoni in 1817 in the tomb of Seti I near Thebes. It was purchased by Sir John Soane, having previously been offered to the British Museum..

When cut in thin sheets, alabaster is translucent enough to be used for small windows, and has been used so in medieval churches, especially in Italy. Large alabaster sheets are used extensively in the Cathedral of Our Lady of the Angels (dedicated 2002) of theLos Angeles (California) Archdiocese. The cathedral incorporates special cooling to prevent the panes from overheating and turning opaque.

Calcite alabaster is either a stalagmitic deposit, from the floor and walls of limestone caverns, or a kind of travertine, similarly deposited in springs of calcareous water. Its deposition in successive layers gives rise to the banded appearance that the marble often shows on cross-section, whence it is known as onyx-marble or alabaster-onyx, or sometimes simply as onyx— a term which should, however, be restricted to siliceous minerals. Egyptian alabaster has been extensively worked near Suez and near Assiut; there are many ancient quarries in the hills overlooking the plain of Tell el Amarna. The Algerian onyx-marble has been largely quarried in the province of Oran. In Mexico, there are famous deposits of a delicate green variety at La Pedrara, in the district ofTecali, near Puebla.. Onyx-marble occurs also in the district of Tehuacán and at several localities in CaliforniaArizonaUtah,Colorado andVirginia.

Gypsum alabaster

Statue made of Alabaster,Yemen

When the term “alabaster” is used without any qualification, it invariably means a fine-grainedvariety of gypsum. This mineral, or alabaster proper, occurs in England. However, thousands of gypsum alabaster artifacts dating to the late 4th millennium BC have been found in Tell Brak(present day Nagar), in Syria.[5] And in Mesopotamia, a gypsum alabaster sculpture, believed to represent the god Abu, dates to the first half of the 3rd millennium BC.[6]

Mineral alabaster occurs in England in the Keuper marls of the Midlands, especially atChellaston in Derbyshire, at Fauld inStaffordshire and near Newark in Nottinghamshire. All these localities have been extensively worked. In the 15th century its carving into icons andaltarpieces was a valuable local industry in Nottingham, as well as a major English export. Besides examples of these still in Britain (especially at the Nottingham Castle Museum,British Museum and Victoria and Albert Museum), that trade in itself (rather than just the antiques trade) has scattered examples as far afield as the Musée de Cluny, Spain and Scandinavia.

Alabaster is also found, though in subordinate quantity, at Watchet in Somerset, near Penarthin Glamorganshire, and elsewhere. InCumbria it occurs largely in the New Red rocks, but at a lower geological horizon. The alabaster of Nottinghamshire and Derbyshire is found in thick nodular beds or “floors” in spheroidal masses known as “balls” or “bowls,” and in smaller lenticular masses termed “cakes.” At Chellaston, where the alabaster is known as “Patrick,” it has been worked into ornaments under the name of “Derbyshire spar” — a term more properly applied to fluorspar.

Black alabaster

Black Alabaster is a rare form of the gypsum-based mineral found in only three veins in the world, one each in Oklahoma (USA),Italy, and the People’s Republic of China.

Alabaster Caverns State Park, near Freedom, Oklahoma is home to a natural gypsum cave in which much of the gypsum is in the form of alabaster. There are several types of alabaster found at the site, including pink, white, and the rare black alabaster.


This alabaster sculpture is untreated: its translucency and satin lustre are preserved. Its base is of marble.

The finer kinds of alabaster are largely employed as an ornamental stone, especially forecclesiastical decoration and for the rails of staircases and halls. Its softness enables it to be readily carved into elaborate forms, but its solubility in water renders it unsuitable for outdoor work. The purest alabaster is a snow-white material of fine tiniforni grain, but it is often associated with an oxide of iron, which produces brown clouding and veining in the stone. The coarser varieties of alabaster are converted by calcination into plaster of Paris, whence they are sometimes known as “plaster stone.”

On the continent of Europe, the centre of the alabaster trade is Florence, ItalyTuscanalabaster occurs in nodular masses embedded in limestone, interstratified with marls ofMiocene and Pliocene age. The mineral is largely worked by means of underground galleries, in the district of Volterra. Several varieties are recognized — veined, spotted, clouded, agatiform, and others. The finest kind, obtained principally from Castellina, is sent to Florence for figure-sculpture, while the common kinds are carved at a very cheap rate locally into vases, clock-cases and various ornamental objects, in which a large trade is carried on, especially in Florence, Pisa and Livorno.

In order to diminish the translucency of the alabaster and to produce an opacity suggestive of true marble, the statues are immersed in a bath of water and gradually heated nearly to the boiling-point — an operation requiring great care, for if the temperature is not carefully regulated, the stone acquires a dead-white, chalky appearance. The effect of heating appears to be a partial dehydration of the gypsum. If properly treated, it very closely resembles true marble and is known as marmo di Castellina. Sulphate of lime (gypsum) was used also by the ancients, and was employed, for instance, in Assyrian sculpture, so that some of the ancient alabaster is identical with the modern stone.

Alabaster may be stained by digesting it, after being heated in various pigmentary solutions. In this way a good imitation of coral has been produced (alabaster coral).




Pillar coralDendrogyra cylindricus
Scientific classification
Kingdom: Animalia
Phylum: Cnidaria
Class: Anthozoa
Ehrenberg, 1831
Extant Subclasses and Orders
[1][2] See Anthozoa for details

Corals are marine organisms from the class Anthozoa and exist as small sea anemone-like polyps, typically in colonies of many identical individuals. The group includes the important reef builders that are found in tropical oceans, which secretecalcium carbonate to form a hard skeleton.

A coral “head”, commonly perceived to be a single organism, is formed from myriads of individual but genetically identicalpolyps, each polyp only a few millimeters in diameter. Over thousands of generations, the polyps lay down a skeleton that is characteristic of their species. An individual head of coral grows by asexual reproduction of the individual polyps. Corals also breed sexually by spawning, with corals of the same species releasing gametes simultaneously over a period of one to several nights around a full moon.

Although corals can catch small fish and animals such as plankton using stinging cells on their tentacles, these animals obtain most of their nutrients from photosynthetic unicellular algae called zooxanthellae. Consequently, most corals depend on sunlight and grow in clear and shallow water, typically at depths shallower than 60 m (200 ft). These corals can be major contributors to the physical structure of the coral reefs that develop in tropical and subtropical waters, such as the enormous Great Barrier Reef off the coast of QueenslandAustralia. Other corals do not have associated algae and can live in much deeper water, with the cold-water genus Lophelia surviving as deep as 3000 m.[3] Examples of these can be found living on the Darwin Mounds located north-west of Cape WrathScotland. Corals have also been found off the coast ofWashington State and the Aleutian Islands in Alaska.

Corals coordinate behaviour by communicating with each other.[4]


Main article: Anthozoa

Corals belong to the class Anthozoa and are divided into two subclasses, depending on the number of tentacles or lines of symmetry, and a series of orders corresponding to their exoskeleton, nematocyst type and mitochondrial genetic analysis.[1][2][5] Those with eight tentacles are called octocorallia or Alcyonariaand comprise soft coralssea fans and sea pens. Those with more than eight in a multiple of six are called hexacorallia or Zoantharia. This group includes reef-building corals (Scleractinians), sea anemones andzoanthids.


Anatomy of a coral polyp

While a coral head appears to be a single organism, it is actually a head of many individual, yet genetically identicalpolyps. The polyps are multicellular organisms that feed on a variety of small organisms, from microscopic plankton to small fish.

Polyps are usually a few millimeters in diameter, and are formed by a layer of outer epithelium and inner jellylike tissue known as the mesoglea. They are radially symmetrical with tentacles surrounding a central mouth, the only opening to the stomach or coelenteron, through which both food is ingested and waste expelled.

The stomach closes at the base of the polyp, where the epithelium produces an exoskeleton called the basal plate or calicle (L. small cup). This is formed by a thickened calciferous ring (annular thickening) with six supporting radial ridges (as shown below). These structures grow vertically and project into the base of the polyp. When polyps are physically stressed, they contract into the calyx so that virtually no part is exposed above the skeletal platform. This protects the organism from predators and the elements (Barnes, R.D., 1987; Sumich, 1996).[6][7]

The polyp grows by extension of vertical calices which are occasionally septated to form a new, higher, basal plate. Over many generations this extension forms the large calciferous (Calcium containing) structures of corals and ultimately coral reefs.

Formation of the calciferous exoskeleton involves deposition of the mineral aragonite by the polyps fromcalcium ions they acquire from seawater. The rate of deposition, while varying greatly across species and environmental conditions, can be as much as 10 g / m² of polyp / day (0.3 ounce / sq yd / day). This is light dependent, with night-time production 90% lower than that during the middle of the day.[8]

Nematocyst discharge: A dormant nematocyst discharges response to nearby prey touching the cnidocil, the operculum flap opens and its stinging apparatus fires the barb into the prey leaving a hollow filament through which poisons are injected to immobilise the prey, then the tentacles manoeuvre the prey to the mouth.

The polyp’s tentacles trap prey using stinging cells called nematocysts. These are cells modified to capture and immobilize prey, such as plankton, by injecting poisons, firing very rapidly in response to contact. These poisons are usually weak but in fire corals are potent enough to harm humans. Nematocysts can also be found in jellyfish and sea anemones. The toxins injected by nematocysts immobilize or kill prey, which can then be drawn into the polyp’s stomach by the tentacles through a contractile band of epithelium called the pharynx.

The polyps interconnect by a complex and well developed system of gastrovascular canals allowing significant sharing of nutrients and symbiotes. In soft corals these range in size from 50-500 μm in diameter and to allow transport of both metabolites and cellular components.[9]

Close-up of Montastrea cavernosa polyps. Tentacles are clearly visible.

Aside from feeding on plankton, many corals as well as other cnidarian groups such as sea anemones (e.g.Aiptasia), form asymbiotic relationship with a class of algaezooxanthellae, of the genus Symbiodinium. The sea anemone Aiptasia, while considered a pest among coral reef aquarium hobbyists, has served as a valuable model organism in the scientific study of cnidarian-algal symbiosis. Typically a polyp harbors one particular species of algae. Via photosynthesis, these provide energy for the coral, and aid in calcification.[10] The algae benefit from a safe environment, and use the carbon dioxide and nitrogenous waste produced by the polyp. Due to the strain the algae can put on the polyp, stress on the coral often triggers ejection of the algae, known on a large scale as coral bleaching, as it is the algae that contribute to the brown coloration of corals; other colors, however, are due to host coral pigments, such as GFPs (green fluorescent protein). Ejecting the algae increases the polyps’ chances of surviving stressful periods – they can regain the algae at a later time. If the stressful conditions persist, the corals eventually die.[11]


Corals can be both gonochoristic (unisexual) and hermaphroditic, each of which can reproduce sexually and asexually. Reproduction also allows coral to settle new areas.


Life cycles of broadcasters and brooders.

Corals predominantly reproduce sexually, with 25% of hermatypic corals (stony corals) forming single sex (gonochoristic) colonies, whilst the rest are hermaphroditic.[12] About 75% of all hermatypic corals “broadcast spawn” by releasing gametes – eggs and sperm – into the water to spread offspring over large distances. The gametes fuse during fertilisation to form a microscopic larvum called a planula, typically pink and elliptical in shape; a moderately sized coral colony can form several thousands of these larvae per year to overcome the huge odds against formation of a new colony.[13]

The planula swims towards light, exhibiting positive phototaxis, to surface waters where they drift and grow for a time before swimming back down to locate a surface on which it can attach and establish a new colony. At many stages of this process there are high failure rates, and even though millions of gametes are released by each colony very few new colonies form. The time from spawning to settling is usually 2 or 3 days, but can be up to 2 months.[14] The larva grows into a coral polyp and eventually becomes a coral head by asexual budding and growth, creating new polyps.

A male star coralMontastraea cavernosa, releases sperm into the water.

Corals that do not broadcast their eggs are called brooders, this is the case for most non-stony corals. These corals release sperm but harbour eggs, allowing larger, negatively buoyant, planulae to form which the polyp later releases ready to settle.[10] The larva grows into a coral polyp and eventually becomes a coral head by asexual budding.

Synchronous spawning is very typical on a coral reef and often, even when multiple species are present, all the corals on the reef release gametes the same night. This synchrony is essential so that male and female gametes can meet and form planula. The cues that guide the release are complex, but over the short term involve lunar changes, sunset time, and possibly chemical signalling.[12] Synchronous spawning may have the result of forming coral hybrids and is perhaps involved in coral speciation.[15] In some places the coral spawn can be dramatic, usually occurring at night, where the usually clear water becomes cloudy with gametes.

Corals must rely on environmental cues, varying from species to species, to determine the proper time to release gametes into the water. Corals use two methods for sexual reproduction, which differ in whether the female gametes are released:

  • Broadcasters, the majority of which mass spawn, rely heavily on environmental cues, because in contrast to brooders they release both sperm and eggs into the water. The corals use long-term cues such as day length, water temperature, and/or rate of temperature change. The short-term cue is most often the lunar cycle, with the sunset cuing the time of release.[12] About 75% of coral species are broadcasters, the majority of which are hermatypic, or reef-building corals.[12] The positively buoyant gametes float towards the surface where fertilization occurs to produce planulalarvae. The planula larvae swim towards the surface light to enter into currents, where they remain usually for two days, but can be up to three weeks, and in one known case two months,[14] after which they settle and metamorphose into polyps and form colonies.
  • Brooders are most often ahermatypic (non-reef building) in areas of high current or wave action. Brooders release only sperm, which is negatively buoyant, and can store unfertilized eggs for weeks, lowering the need for mass synchronous spawning events, which do sometimes occur.[12] After fertilization the corals release planula larvae which are ready to settle.


Calices (basal plates) ofOrbicella annularisshowing two methods of multiplication: gemmation (small central calicle) and division (large double calicle).

Within a coral head the genetically identical polyps reproduce asexually to allow colony growth. This is achieved either through gemmation (budding) or through division, both shown in the diagrams of Orbicella annularis. Budding involves a new polyp growing from an adult, whereas division forms two polyps each as large as the original.[13]

  • Budding expands the size of a coral colony. It occurs when a new corallite grows out from the adult polyp. As the new polyp grows it produces a coelenteron (stomach), tentacles and a mouth. The distance between the new and adult polyps grows, and with it the coenosarc (the common body of the colony; see coral anatomy). Budding can occur by means of:
    • Intra-tentacular budding forms from the oral discs of a polyp, meaning that both polyps are the same size and are within the same ring of tentacles.
    • Extra-tentacular budding forms from the base of a polyp, and the new polyp is smaller.
  • Longitudinal division begins with broadening of a polyp, which then divides the coelenteron. The mouth divides and new tentacles form. The two “new” polyps must generate their missing body parts and exoskeleton..
  • Transversal division occurs when polyps and the exoskeleton divide transversally into two parts. This means that one has the basal disc (bottom) and the other has the oral disc (top). The two new polyps must again generate the missing parts.
  • Fission occurs in some corals, especially among the family Fungiidae, where the colony is able to split into two or more colonies during the early stages of their development.

Whole colonies can reproduce asexually through fragmentation or bailout, forming another individual colony with the same genome..

  • Polyp bailout occurs when a single polyp abandons the colony and re-establishes on a new substrate to create a new adult colony..
  • Fragmentation, involves individuals broken from the colony during storms, or other situations where breaking can occur. The separated individuals can start new coral colonies.


Locations of coral reefs

Main article: Coral reef

The hermatypic, stony corals are often found in coral reefs, large calcium carbonate structures generally found in shallow,tropical water. Reefs are built up from coral skeletons and held together by layers of calcium carbonate produced bycoralline algae. Reefs are extremely diverse marine ecosystems being host to over 4,000 species of fish, massive numbers of cnidarians, molluskscrustaceans, and many other animals.[16]


Hermatypic corals

Further information: Scleractinia
Further information: Millepora
Further information: Tubipora
Further information: Heliopora

Hermatype corals or stony corals build reefs. With the help of zooxanthellae, they convert surplus food to calcium carbonate forming a hard skeleton. Hermatype-species include ScleractiniaMilleporaTubiporaand Heliopora[17]

In the Caribbean alone 50 species of uniquely structured hard coral exist. Some of the most well known types being:

  • Brain coral grow to 1.8 meters in width.
  • Acropora and Staghorn coral grow fast and large and are important reef-builders. Staghorn coral displays large antler-like branches and grows in areas with strong surf.
  • Galaxea fascicularis or star coral is another important reef-builder.
  • Pillar coral forms pillars which can grow to 3 meters in height..
  • Leptopsommia or rock coral, appears almost everywhere in the Caribbean[18].

Ahermatypic corals

Further information: Alcyonacea
Further information: Anthipatharia

Ahermatypic corals are corals that have no zooxanthellae and can therefore not build the solid skeletons that form reefs. They include Alcyonaceas, as well as some Anthipatharia-species (Black coralCirripathes,Antipathes). [17] Ahermatypic corals such as sea whipssea feathers, and sea pens [18] are also known as soft corals. Unlike stony corals, they are flexible, moving back and forth in the current, and often are perforated, with a lace-like appearance. Their skeletons are made of protein, rather than calcium. Soft corals are somewhat less plentiful (in the Caribbean, twenty species appear) than stony corals.

Evolutionary history

The fossil coral Heliophyllum hallifrom the Devonian period, found inCanada.

Although corals first appeared in the Cambrian period,[19] some 542 million years ago, fossils are extremely rare until theOrdovician period, 100 million years later, when Rugose and Tabulate corals became widespread.

Tabulate corals occur in the limestones and calcareous shales of the Ordovician and Silurian periods, and often form low cushions or branching masses alongside Rugose corals. Their numbers began to decline during the middle of the Silurian period and they finally became extinct at the end of the Permian period, 250 million years ago. The skeletons of Tabulate corals are composed of a form of calcium carbonate known as calcite.

Rugose corals became dominant by the middle of the Silurian period, and became extinct early in theTriassic period. The Rugose corals existed in solitary and colonial forms, and are also composed of calcite.

The Scleractinian corals filled the niche vacated by the extinct Rugose and Tabulate species. Their fossils may be found in small numbers in rocks from the Triassic period, and become relatively common in theJurassic and later periods. Scleractinian skeletons are composed of a form of calcium carbonate known asaragonite.[20] Although they are geologically younger than the Tabulate and Rugose corals, their aragonitic skeleton is less readily preserved, and their fossil record is less complete..

Timeline of the major coral fossil record and developments from 650 m.y.a. to present.[21][22]

At certain times in the geological past corals were very abundant. Like modern corals, these ancestors built reefs, some of which now lie as great structures in sedimentary rocks.

Fossils of fellow reef-dwellers algae, sponges, and the remains of many echinoidsbrachiopodsbivalves,gastropods, andtrilobites appear along with coral fossils. This makes some corals useful index fossils, enabling geologists to date the age the rocks in which they are found.

Coral fossils are not restricted to reef remnants, and many solitary corals may be found elsewhere, such asCyclocyathus, which occurs in England‘s Gault clay formation.

Environmental influences

A healthy coral reef has a striking level of biodiversity in many forms of marine life.

Corals are highly sensitive to environmental changes. Scientists have predicted that over 50% of the world’scoral reefs may be destroyed by the year 2030;[23] as a result most nations protect them through environmental laws. Algae can overwhelm a coral reef if too many nutrients are present. Coral will also die if the water temperature changes by more than a degree or two beyond its normal range or if the salinity of the water drops. In an early symptom of environmental stress, corals expel their zooxanthellae; without their symbiotic unicellular algae, coral tissues become colorless as they reveal the white of their calcium carbonate skeletons, an event known as coral bleaching.[24]

Many governments now prohibit removal of coral from reefs and use education to inform their populations about reef protection and ecology. However, many other human activities damage reefs, including mooring, fishing, diving, mining and construction.

The narrow niche that coral occupies, and the stony corals‘ reliance on calcium carbonate deposition, means they are susceptible to changes in water pH. The increase in atmospheric carbon dioxide has caused enough dissolution of carbon dioxide to lower the ocean’s pH, in a process known as ocean acidification. Lowered pH reduces the ability of corals to produce calcium carbonate, and at the extreme, can entirely dissolve those skeletons. Without deep and immediate cuts in anthropogenic CO2 emissions, scientists fear that ocean acidification will result in the severe degradation or destruction of coral species and ecosystems.[25]

A section through a coral, dyed to determine growth rate

Climatic variations can cause temperature changes that destroy corals. For example, during the 1997-98 warming event all the hydrozoan Millepora boschmai colonies near Panamá were bleached and died within six years – this species is now thought to be extinct.[26]


Live corals

Local economies near major coral reefs benefit from an abundance of fish and other marine creatures as a food source. Reefs also provide recreational scuba diving and snorkeling tourism. Unfortunately these activities can also have deleterious effects, such as accidental destruction of coral. Coral is also useful as a protection against hurricanes and other extreme weather.

Live coral is highly sought after in the aquarium trade. Provided the proper ecosystem, live coral makes a stunning addition to any salt water aquarium. Soft corals are considered easier to maintain in captivity than hard corals.[27]

Deep sea bamboo corals (Isididae) may be among the first organisms to display the effects of ocean acidification. They produce growth rings similar to those of tree and can provide a view of changes in the condition in the deep sea over time.[28] Other coral biology research presents the possibility that Isididae corals, because of their potential to mimic biological properties, may be usable as living bone implants and in aquatic cultivation.[29]

Coral as a gemstone

Main article: Coral (precious)

Intensely red coral is sometimes called fire coral (but this is not at all the same thing as fire coral). Red coral is very rare now because of overharvesting due to the great demand for perfect red coral in jewelry-making.

Ancient corals

Tabulate coral (a syringoporid); Boone Limestone (LowerCarboniferous) near Hiwasse, Arkansas. Scale bar is 2.0 cm.

Ancient coral reefs on land are often mined for lime or use as building blocks (“coral rag“). Coral rag is an important local building material in places such as the East African coast.

The annual growth bands in bamboo corals and others allow geologists to construct year-by-year chronologies, a form ofincremental dating, which can provide high-resolution records of past climatic andenvironmental changes usinggeochemical techniques.[30]

Certain species of corals form communities called microatolls. The vertical growth of microatolls is limited by average tidal height. By analyzing the various growth morphologies, microatolls can be used as a low resolution record of patterns of sea level change. Fossilized microatolls can also be dated using radioactive carbon dating. Such methods have been used to used to reconstruct Holocene sea levels.[31]


Further images: commons:Category:Coral reefs and commons:Category:Coral

Fungia sp. skeleton

Brain coralDiploria labyrinthiformis

Polyps of Eusmilia fastigiata

Staghorn coral,Acropora

Orange cup coral,Balanophyllia elegans

Brain coral spawning

Brain coral releasing eggs

Fringing coral reef off the coast of EilatIsrael.



Amber pendants. The ovalpendant is 52 by 32 mm (2 by 1.3 inches).

Amber is fossil tree resin, which is appreciated for its color and beauty. Good quality amber is used for the manufacture of ornamental objects and jewelry. Although not mineralized, it is often classified as a gemstone.

A common misconception is that amber is made of tree sap; it is not. Sap is the fluid that circulates through a plant’s vascular system, while resin is the semi-solid amorphous organic substance secreted in pockets and canals through epithelial cells of the plant.

Because it used to be soft and sticky tree resin, amber can sometimes contain insects and even small vertebrates.

Semi-fossilized resin or sub-fossil amber is known as copal.

Amber occurs in a range of different colors. As well as the usual yellow-orange-brown that is associated with the color “amber”, amber itself can range from a whitish color through a pale lemon yellow, to brown and almost black. Other more uncommon colors include red amber (sometimes known as “cherry amber”), green amber, and even blue amber, which is rare and highly sought after.

A lot of the most highly-prized amber is transparent, in contrast to the very common cloudy amber and opaque amber. Opaque amber contains numerous minute bubbles. This kind of amber is known as “bony amber”, even though it is in fact true amber.

Origin of the term

Wood resin, the ancient source of amber

The English word amber stems from the old Arabic word anbargris or ambergris and refers to an oily, perfumed substance secreted by the sperm whale. Middle English ambre > Old French ambre > Medieval Latin ambra (or ambar). It floats on water and is washed up on the beaches. Due to a confusion of terms (see: Abu Zaid al Hassan from Siraf & Sulaiman the Merchant (851), Silsilat-al-Tawarikh (travels in Asia), it came to be the name for fossil resin, which is also found on beaches, and which is lighter than stone, but not light enough to float.

The presence of insects in amber was noticed by the Pliny the Elder in his Naturalis Historiaand led him to the (correct) theory that at some point, amber had to be in a liquid state to cover the bodies of insects. Hence he gave it the expressive name of succinum orgum-stone, a name that is still in use today to describe succinic acid as well as succinite, a term given to a particular type of amber by James Dwight Dana (see below under Baltic Amber).

The Greek name for amber was ηλεκτρον (Electron) and was connected to the Sun God, one of whose titles was Elector or theAwakener.[1] It is discussed by Theophrastus, possibly the first ever mention of the material, and in the 4th century BC. The modern term electron was coined in 1891 by the Irish physicist George Stoney, using the Greek word for amber (and which was then translated as electrum) because of its electrostatic properties and whilst analyzing elementary charge for the first time. The ending -on, common for all subatomic particles, was used in analogy to the word ion.[2][3]

Heating amber will soften it and eventually it will burn, which is why in Germanic languagesthe word for amber is a literal translation of burn-Stone (In German it is Bernstein, in Dutch it is barnsteen etc.). Heated above 200°C, amber suffers decomposition, yielding an “oil of amber”, and leaving a black residue which is known as “amber colophony”, or “amber pitch”; when dissolved in oil ofturpentine or in linseed oil this forms “amber varnish” or “amber lac”.

Amber from the Baltic Sea has been extensively traded since antiquity and in the main land, from where amber was traded 2000 years ago, the natives called it glaes (referring to its see-through similarity to glass).

The Baltic Lithuanian term for amber is Gintaras and Latvian Dzintars. They and the Slavicjantar are thought to originate fromPhoenician jainitar (sea-resin). However, while most Slavic languages, such as Russian and Czech, retain the old Slavic word, in the Polish language, despite still correct, it is used very rarely (even considered archaic) and was replaced by the word bursztyn deriving from the German analogue.

mosquito and a fly in thisBaltic amber necklace are between 40 and 60 million years old

Chemistry of amber

Amber is heterogeneous in composition, but consists of several resinous bodies more or less soluble in alcoholether andchloroform, associated with an insoluble bituminous substance. Amber is a macromolecule by free radical polymerization of several precursors in the labdanefamily, communic acid, cummunol and biformene.[4] These labdanes are diterpenes (C20H32) and trienes which means that the organic skeleton has three alkene groups available forpolymerization. As amber matures over the years, more polymerization will take place as well as isomerization reactions, crosslinking and cyclization. The average composition of amber leads to the general formula C10H16O.

Amber should be distinguished from copal. Molecular polymerisation caused by pressure and heat transforms the resin first into copal and then over time through the evaporation of turpenes it is transformed into amber.

Baltic amber is distinguished from the various other ambers from around the world, by the presence within it of succinic acid,[citation needed] hence Baltic amber is otherwise known as succinite.

Amber in geology

The oldest amber originates from the Upper Carboniferous period approximately 345 million years ago. The oldest known amber containing insects comes from the Lower Cretaceous, approximately 146 million years ago.

Commercially most important are the deposits of Baltic and Dominican amber.[5]

A bee and a leaf inside amber

Baltic amber or succinite (historically documented as Prussian amber) is found as irregular nodules in a marine glauconitic sand, known as blue earth, occurring in the Lower Oligocenestrata of Samland in Prussia (Latin: Sambia), in historical sources also referred to asGlaesaria. After 1945 this territory around Königsberg was turned into Kaliningrad Oblast,Russia, where it is now systematically mined.[6] It appears, however, to have been partly derived from yet earlier Tertiary deposits (Eocene); and it occurs also as a derivative mineral in later formations, such as the drift. Relics of an abundant flora occur as inclusions trapped within the amber while the resin was yet fresh, suggesting relations with the flora of EasternAsia and the southern part of North America.Heinrich Göppert named the common amber-yielding pine of the Baltic forests Pinites succiniter, but as the wood, according to some authorities, does not seem to differ from that of the existing genus it has been also calledPinus succinifera. It is improbable, however, that the production of amber was limited to a single species; and indeed a large number of conifers belonging to different genera are represented in the amber-flora.

Dominican amber is considered retinite, since it has no succinic acid. There are three main sites in the Dominican Republic: La Cordillera Septentrional, in the north, Bayaguana and Sabana, in the east. In the northern area, the amber-bearing unit is formed of clastic rocks, sandstone accumulated in a deltaic or even deep-water environment. The oldest, and hardest of this amber comes from the mountain region north of Santiago area, from the mines at La Cumbre, La Toca, Palo Quemado, La Bucara, and Los Cacaos mining sites in the Cordillera Septentrional not far from Santiago. Amber in these mountains is tightly embedded in a lignite layer of sandstone.

There is also amber in the south-eastern Bayaguana/Sabana area. It is softer, sometimes brittle and suffers oxidation after being taken from the mines, therefore less expensive. There is also copal found with only an age of 15-17 million years. In the eastern area, the amber is found in a sediment formation of organic-rich laminated sand, sandy clay, intercalated lignite as well as some solated beds of gravel and calcarenite.

Both Baltic and Dominican amber are rich sources of fossils and give much information about life in the ancient forests. [7]

Amber from the Middle Cretaceous is known from Ellsworth County, Kansas. This approximately 100 million year old amber has inclusions of bacteria and amoebae. They are morphologically very close to Leptothrix, and the modern genera Pontigulasia andNebela. Morphological stasis is considered to be confirmed.[8]

Amber inclusions

A spider trapped in amber

Ant trapped in amber.

The resin contains, in addition to the beautifully preserved plant-structures, remains of insects, spiders, annelids, frogs,[9]crustaceans, marine microfossils[10] and other small organisms which were trapped by the sticky surface and became enveloped while the exudation was fluid. In most cases the organic structure has disappeared, leaving only a cavity, with perhaps a trace ofchitin. Even hair and feathers have occasionally been represented among the enclosures. Fragments of wood frequently occur, with the tissues well-preserved by impregnation with the resin; while leaves, flowers and fruits are occasionally found in marvelous perfection. Sometimes the amber retains the form of drops and stalactites, just as it exuded from the ducts and receptacles of the injured trees. It is thought that, in addition to exuding onto the surface of the tree, amber resin also originally flowed into hollow cavities or cracks within trees, thereby leading to the development of large lumps of amber of irregular form.[11]

The abnormal development of resin has been called succinosis. Impurities are quite often present, especially when the resin dropped on to the ground, so that the material may be useless except for varnish-making, whence the impure amber is called firniss. Enclosures ofpyrites may give a bluish color to amber. The so-called black amber is only a kind of jetBony amber owes its cloudy opacity to minute bubbles in the interior of the resin.

Not all amber is translucent, becoming transparent when the surfaces are polished, thus revealing inclusions. The technique of inspecting darkly clouded and even opaque amber for inclusions, through bombarding it with high-energy, high-contrast, high-resolution x-rays, is being developed at the European Synchrotron Radiation Facility.[12] Nearly 360 fossil invertebrates have been discovered from opaque amber found at Charentes, France: primitive wasps, flies, ants and spiders, particularly those measuring just a few millimeters. Three-dimensional images of the trapped organisms are built up through microtomography, showing detail on the scales of micrometres. An enlarged plastic three-dimensional model can be obtained of an organism that has remained embedded in the amber, suggesting alternative means of cataloguing new species trapped in amber.

Amber locations

Baltic amber

Lithuanian girls in the national dress, which includes an amber necklace.

Baltic amber has a very wide distribution, extending over a large part of northern Europe and occurring as far east as the Urals.

Baltic amber yields on dry distillation succinic acid, the proportion varying from about 3% to 8%, and being greatest in the pale opaque or bony varieties. The aromatic and irritating fumes emitted by burning amber are mainly due to this acid. Baltic amber is distinguished by its yield of succinic acid, hence the name succinite proposed by Professor James Dwight Dana, and now commonly used in scientific writings as a specific term for the Prussian amber. Succinite has a hardness between 2 and 3, which is rather greater than that of many other fossil resins. Its specific gravity varies from 1.05 to 1.10. An effective tool for Baltic amber analysis is IR spectroscopy. It enables the distinction between Baltic and non-Baltic amber varieties because of a specific carbonylabsorption and it can also detect the relative age of an amber sample. On the other hand, it has been suggested by scientists that succinic acid is no original component of amber, but a degradation product of abietic acid. (Rottlaender, 1970)

Although amber is found along the shores of a large part of the Baltic Sea and the North Sea, the great amber-producing area for many centuries was the promontory of Sambia or Samland, the coast around Königsberg in Prussia, since 1945 part of Russia. About 90% of the world’s extractable amber is still located in the Kaliningrad Oblast of Russia on the Baltic Sea.[13] Pieces of amber torn from the seafloor are cast up by the waves, and collected at ebb-tide. Sometimes the searchers wade into the sea, furnished with nets at the end of long poles, which they drag in the seaweed containing entangled masses of amber; or they dredge from boats in shallow water and rake up amber from between the boulders. Divers have been employed to collect amber from the deeper waters. Systematic dredging on a large scale was at one time carried on in the Curonian Lagoon by Messrs Stantien and Becker, the great amber merchants of Königsberg. At the present time extensive mining operations are conducted in quest of amber. The pit amberwas formerly dug in open works, but is now also worked by underground galleries. The nodules from the blue earth have to be freed from matrix and divested of their opaque crust, which can be done in revolving barrels containing sand and water. The sea-worn amber has lost its crust, but has often acquired a dull rough surface by rolling in sand.

Since the establishment of the Amber Road, amber known as “Prussian gold” (which is now also referred to as “Lithuanian gold”) has substantially contributed economically and culturally. Amber jewellery and amberware is offered to foreign tourists in mostsouvenir shops as distinctive to Lithuania and its cultural heritage. The seaside town of Palanga has the Palanga Amber Museumdedicated to amber. Amber can also be found in Latvia as well as Denmark,northern GermanyPoland, and, since the takeover of Prussia in 1945, also in Russia.

Dominican amber

A rare set of Arab worry beads(masbaha) made of Dominicanblue amber.

Dominican amber differentiates itself from Baltic amber by being mostly transparent and often containing a higher number of fossilinclusions. This has enabled the detailed reconstruction of the ecosystem of a long-vanished tropical forest.[14] Resin from the extinct species Hymenaea protera is the source of Dominican amber and probably of most amber found in the tropics. It is not “succinite” but “retinite“. [15] In contrast to much Baltic amber, Dominican amber found on the world market is natural amber the way it comes from the mines, and has not been enhanced or received any chemical or physical change. The age of Dominican amber is up to 40 million years. [16]

Although all Dominican amber is fluorescent, the rarest Dominican amber is blue amber. It turns blue in natural sunlight and any other partially or wholly ultraviolet light source. In long-wave UV light it has a very strong reflection, almost white. Only about 100 kilos of this fossilized tree is found per year, which makes it valuable and expensive.[17]

Dragon carved from Dominican blue amber

Dominican amber, and especially Dominican blue amber, is mined through bell pitting, which is highly dangerous for workers due to the risk of the excavation walls collapsing on them. [18]Bell pitting is basically a foxhole dug with whatever tools are available. Machetes do the start, some shovels, picks and hammers may participate eventually. The pit itself goes as deep as possible or safe, sometimes vertical, sometimes horizontal, but never level. It snakes into hill sides, drops away, joins up with others, goes straight up and pops out elsewhere. Rarely are the pits large enough to stand in, and then only at the entrance. Miners crawl around on their knees using short-handled picks, shovels and machetes. The amber that is found is either directly sold as rough or raw pieces or cut and polished without any additional treatments or enhancements.[14]

The most common use for Dominican amber is as ornaments and jewellery, while the more valuable enclosures and colorations become priced exhibition pieces both in private and public collections. [19] In the Far East, the rare blue Amber has been masterfully worked into artistic carvings. Others have used blue amber to make jewellery that can be especially attractive for its naturalfluorescence under UV lights. In the Muslim world, Dominican amber and particularly blue amber beads have found their way into another use as Prayer beads andworry beads, since Dominican amber can very easily be worked.[20][21]

Other locations

Amber deposits are found around the world. Some are much older than the well known amber deposits in the Baltic countries and the Dominican Republic, others are much younger. Some amber is considered to be up to 345 million years old (Northumberland USA).

A lesser known source of amber is in the Ukraine, within a marshy forested area on the Volyhn-Polesie border. Due to the shallow depth at which this amber is found it can be extracted with the simplest of tools, and this has led to an economy of amber poaching under cover of the forest. This Ukrainian amber has a wide range of colors, and was used in the restoration of Amber Room in the Empress Catherine’s palace in Saint Petersburg (see below).

Sailboat made entirely from amber in a gift shop

Rolled pieces of amber, usually small but occasionally of very large size, may be picked up on the east coast of England, having probably been washed up from deposits under the North Sea. Cromer is the best-known locality, but it occurs also on other parts of the Norfolk coast, such as Great Yarmouth, as well as SouthwoldAldeburgh and Felixstowe in Suffolk, and as far south as Walton-on-the-Naze in Essex, whilst northwards it is not unknown in Yorkshire. On the other side of the North Sea, amber is found at various localities on the coast of theNetherlands and Denmark. On the shores of the Baltic it occurs not only on the German and Polish coast but in the south of Sweden, in Bornholm and other islands, and in southernFinland. Some of the amber districts of the Baltic and North Sea were known in prehistoric times, and led to early trade with the south of Europe through the Amber Road. Amber was carried to Olbia on the Black Sea, Massilia (today Marseille) on the Mediterranean, and Adriaat the head of the Adriatic; and from these centres it was distributed over the Ancient Greekworld.

Amber is found in Switzerland, Austria and France. Amber from the Swiss Alps is about 55 – 200 million years old, amber from Golling about 225 – 231 million years. The well-known Sicilian Amber (Simetit – copal) is just 10 – 20 million years old.

In Africa, copal is found in the coastal countries of East and West Africa, but especially onMadagascar. This so-called MadagascarAmber is only 1,000 – 10,000 years old and consists of the solidified resin of the amber pine. Nigeria also has amber, which is about 60 million years old.

In Asia amber can be found especially in Burma (former Burma / Myanmar) as Burmit. It is about 50 million years and the Lebanon amber 130 – 135 million years old. Amber of the Australian-oceanic area can be found in New Zealand and Borneo (Sarawak amber). They are about 20 – 60, part 70 – 100 million years old.

Rare polished transparent Borneo amber from Sabah, Malaysia

Amber is also found to a limited extent in the United States, as in the green-sand of New Jersey, but it has little economic value. Middle Cretaceous amber has also been found inEllsworth County, Kansas. It has little value for jewelry makers, but is very valuable to biologists. The source of this amber is under a man-made lake.

A fluorescent amber occurs also in the southern state of Chiapas in Mexico, and is used for eye-catching jewellery. In Central America, the Olmec civilization was mining amber around 3000 B.C. There are legends in Mexico that mention the use of amber in adorning, consuming and using it for stress reduction as a natural remedy.

Indonesia is also a rich source of amber with large fragments being unearthed in both Java and Bali.

Amber treatments

Amber, 12 cm diameter

The Vienna amber factories which use pale amber to manufacture pipes and other smoking tools, turn it on a lathe and polish it with whitening and water or with rotten stone and oil. The final lustre is given by friction with flannel.

When gradually heated in an oil-bath, amber becomes soft and flexible. Two pieces of amber may be united by smearing the surfaces with linseed oil, heating them, and then pressing them together while hot. Cloudy amber may be clarified in an oil-bath, as the oil fills the numerous pores to which the turbidity is due. Small fragments, formerly thrown away or used only for varnish, are now used on a large scale in the formation of “amberoid” or “pressed amber”. The pieces are carefully heated with exclusion of air and then compressed into a uniform mass by intense hydraulic pressure; the softened amber being forced through holes in a metal plate. The product is extensively used for the production of cheap jewellery and articles for smoking. This pressed amber yields brilliant interference colors in polarized light. Amber has often been imitated by other resins like copal and kauri, as well as by celluloid and even glass. Baltic amber is sometimes colored artificially, but also called “true amber”.

Often amber (particularly with insect inclusions) is counterfeited using a plastic resin. A simple test consists of touching the object with a heated pin and determining if the resultant odor is of wood resin. If not, the object is counterfeit, although a positive test may not be conclusive owing to a thin coat of real resin. Often counterfeits will have a too perfect pose and position of the trapped insect.

Amber art and ornament

Unpolished amber stones

Amber was much valued as an ornamental material in very early times. It has been found inMycenaean tombs; it is known from lake-dwellings in Switzerland, and it occurs with Neolithicremains in Denmark, whilst in England it is found with interments of the bronze age.

The so-called Hove amber cup, a cup turned in amber from a bronze-age barrow at Hove is now in the Brighton Museum.

Beads of amber are found with Anglo-Saxon relics in the south of England. Amber was valued as an amulet and it is still believed to possess medicinal properties.

Amber is used for beads and ornaments, and for cigar-holders and the mouth-pieces of pipes. It is regarded by the Turks as specially valuable, inasmuch as it is said to be incapable of transmitting infection as the pipe passes from mouth to mouth. The variety most valued in the East is the pale straw-colored, slightly cloudy amber. Some of the best qualities are sent toVienna for the manufacture of smoking appliances.

The Amber Room was reconstructed from theKaliningrad amber.

The Amber Room was a collection of chamber wall panels commissioned in 1701 for the king of Prussia, then given to Tsar Peter the Great. The room was hidden in place from invadingNazi forces in 1941, who upon finding it in the Catherine Palace, disassembled it and moved it to Königsberg. What happened to the room beyond this point is unclear, but it may have been destroyed when the Russians burned the German fortification where it was stored. It is presumed lost. It was re-created in 2003.[22]

Amber Frog Violin Bow

The Amber Frog bow by Keith Peck made in 1996/97 commissioned by Gennady Filimonov.

Baltic amber has been used to create the “frog” part of a Violin bow. It was commissioned by Gennady Filimonov and made by the late American Master Bowmaker Keith Peck [23]

The Amber Frog / Picture bow (copy of F.N. Voirin), is the first documented amber frog bow (made in 1996-97) , that was (and is) a complete success. It is still being played by Gennady Filimonov




Rhodochrosite from Sweet Home MineAlma, Colorado, USA
Category Mineral species
Chemical formula MnCO3
Molar mass 114.95 g/mol
Color Red to pink, Brown to yellow, gray to white
Crystal habit Massive to well crystaline
Crystal system Trigonal -HexagonalScalenohedral
Twinning on the {0112} uncommon
Cleavage on the [1011] perfect
Fracture uneven, conchoidal
Tenacity brittle
Mohs Scalehardness 3.5-4
Luster Vitreous
Streak White
Diaphaneity Transparent to translucent
Density 3.7 g/cm³
Optical properties Uniaxial (-)
Birefringence δ = 0.218
Pleochroism weak
Ultravioletfluorescence None

Pink is the most common color of Rhodochrosite. Specimen mined near Silverton, Colorado

Rhodochrosite is a manganese carbonate mineral with chemical composition MnCO3. In its (rare) pure form, it is typically a rose-red color, but impure specimens can be shades of pink to pale brown. The streak is white. Its Mohs hardness varies between 3.5 and 4. Its specific gravity is 3.5 to 3.7. It crystallizes in the trigonal system. The cleavage is typical rhombohedral carbonate cleavage in three directions. Crystal twinning often is present. It is transparent to translucent with refractive indices of =1.814 to 1.816,=1.596 to 1.598. It is often confused with the manganese silicate, rhodonite, but is distinctly softer.

Rhodochrosite forms a complete solid solution series with iron carbonate (siderite). Calcium, (as well as magnesium and zinc, to a limited extent) frequently substitutes for manganese in the structure, leading to lighter shades of red and pink, depending on the degree of substitution. It is for this reason that the most common color encountered is pink.

Rhodochrosite occurs as a hydrothermal vein mineral along with other manganese minerals in low temperature ore deposits as in the silver mines of Romania where it was first found. Banded rhodochrosite is mined in Capillitas, Argentina. Catamarca, Argentina has an old Incan silver mine that has produced fine stalactitic examples of rhodochrosite that are unique and very attractive. Cut cross-sections reveal concentric bands of light and dark rose colored layers.. These specimens are carved and used for many ornamental purposes.[3]

Its main use is as an ore of manganese which is a key component of low-cost stainless steel formulations and certain alluminium alloys. Quality banded specimens are often used for decorative stones and jewelry. Due to its being relatively soft, and having perfect cleaveage, it is very difficult to cut, and therefore rarely found faceted in jewelry.

It was first described in 1813 in reference to a sample from Cavnic, Maramureş, present-dayRomania. According to Dimitrescu and Radulescu, 1966 and to Papp, 1997, this mineral was described for the first time in Sacaramb, Romania, not in Cavnic, Romania. The name is derived from the Greek word for rose-colored.

Colorado officially named rhodochrosite as its state mineral in 2002 based on a proposal by a local high school (Platte Canyon High School in Bailey,Colorado). The reason for this lies in the fact that while the mineral is found worldwide, large red crystals are found only in a few places on earth, and some of the best specimens have been found in the Sweet Home Mine near Alma, Colorado.

The Alma King is the largest known rhodochrosite crystal; it was found in theSweet Home Mine near Alma, Colorado. It is on display in the Denver Museum of Nature and Science.

The Incas believed that rhodochrosite is the blood of their former rulers, turned to stone, therefore it is sometimes called “Rosa del Inca” or “Inca Rose”.[4][5]

Rhodochrosite and silver mining

Manganese carbonate is extremely destructive to the amalgamation process used in the concentration of silver ores, and so until quality mineral specimens became highly sought after by collectors, they




Category feldspartectosilicate
Chemical formula (Ca,Na)(Al,Si)4O8, whereCa/(CaNa) (%Anorthite) is between 50%-70%
Crystal system triclinic
Twinning common
Cleavage three directions
Streak white
Specific gravity 2.71 to 2.74
Refractive index 1.555 to 1.575
Other characteristics iridescence

Detail of Labradorite

Labradorite ((Ca,Na)(Al,Si)4O8), a feldspar mineral, is an intermediate to calcic member of the plagioclase series. It is usually defined as having “%An” (anorthite) between 50 and 70. The specific gravity ranges from 2.71 to 2.74. The streak is white, like most silicates. Therefractive index ranges from 1.555 to 1.575. Twinning is common. As with all plagioclase members the crystal system is triclinic and three directions of cleavage are present two of which form nearly right angle prisms. It occurs as clear, white to gray, blocky to lath shaped grains in common mafic igneous rocks such as basalt and gabbro, as well as in anorthosites.

The geological type area for labradorite is Paul’s Island near the town of Nain in Labrador,Canada. It occurs in large crystal masses in anorthosite and shows an iridescence or play of colors. The iridescence is the result of light refracting within lamellar intergrowths resulting from phase exsolution on cooling in the Boggild miscibility gap, An48-An58.

Gemstone varieties of labradorite exhibiting a high degree of iridescence are called spectrolite;moonstone and sunstone are also commonly used terms, and high-quality samples with good iridescent qualities are desired for jewelry



Potassium feldspar crystals in a granite, eastern Sierra Nevada, Rock Creek Canyon, California. Scale bar is 2.0 cm.
Category tectosilicate
Chemical formula KAlSi3O8NaAlSi3O8-CaAl2Si2O8
Color pink, white, gray, brown
Crystal system triclinic or monoclinic
Twinning tartancarlsbad, etc
Cleavage three
Fracture along cleavage planes
Mohs Scalehardness 6
Luster vitreous
Diaphaneity opaque
Birefringence first order
Pleochroism none
Other characteristics exsolution lamellae common
This article is about a mineral. For the Malcolm in the Middle character, see List of characters in Malcolm in the Middle#Recurring characters.

Lunar Ferroan Anorthosite #60025 (Plagioclase Feldspar). Collected by Apollo 16 from the Lunar Highlands nearDescartes Crater. This sample is currently on display at the National Museum of Natural Historyin Washington, DCUnited States. (Unknown scale.)

Feldspars (KAlSi3O8NaAlSi3O8CaAl2Si2O8) are a group of rock-forming tectosilicateminerals which make up as much as 60% of the Earth‘s crust.[1]

Feldspars crystallize from magma in both intrusive and extrusive igneous rocks, as veins, and are also present in many types ofmetamorphic rock.[2] Rock formed entirely of plagioclasefeldspar (see below) is known as anorthosite.[3] Feldspars are also found in many types ofsedimentary rock.[4]


Feldspar is derived from the German Feld, field, and Spat, a rock that does not contain ore. “Feldspathic” refers to materials that contain feldspar. The alternative spelling, felspar, has now largely fallen out of use.[5]


Compositional phase diagram of the different minerals that constitute the feldspar solid solution.


Alkali feldspar perthite (7cm long X 3cm width).

This group of minerals consists of framework or tectosilicates. Compositions of major elements in common feldspars can be expressed in terms of three endmembers:

Potassium-Feldspar (K-spar) endmember KAlSi3O8[1]

Albite endmember NaAlSi3O8[1]

Anorthite endmember CaAl2Si2O8[1]

Solid solutions between K-feldspar and albite are called alkali feldspar.[1] Solid solutions between albite and anorthite are calledplagioclase,[1] or more properly plagioclase feldspar. Only limited solid solution occurs between K-feldspar and anorthite, and in the two other solid solutions, immiscibility occurs at temperatures common in the crust of the earth. Albite is considered both a plagioclase and alkali feldspar. In addition to albite, barium feldspars are also considered both alkali and plagioclase feldspars. Barium feldspars form as the result of the replacement of potassium feldspar.

Alkali Feldspars

The alkali feldspars are as follows:

Sanidine is stable at the highest temperatures, and microcline at the lowest.[7][6] Perthite is a typical texture in alkali feldspar, due toexsolution of contrasting alkali feldspar compositions during cooling of an intermediate composition. The perthitic textures in the alkali feldspars of many granites can be seen with the naked eye.[9] Microperthitic textures in crystals are visible using a light microscope, whereas cryptoperthitic textures can only be seen using an electron microscope.

Plagioclase Feldspars


The plagioclase feldspars are triclinic. The plagioclase series follows (with percent anorthite in parentheses):

Intermediate compositions of plagioclase feldspar also may exsolve to two feldspars of contrasting composition during cooling, but diffusion is much slower than in alkali feldspar, and the resulting two-feldspar intergrowths typically are too fine-grained to be visible with optical microscopes. The immiscibility gaps in the plagioclase solid solution are complex compared to the gap in the alkali feldspars. The play of colors visible in some feldspar of labradorite composition is due to very fine-grained exsolution lamellae.

Barium Feldspars

The barium feldspars are monoclinic and comprise the following:

Feldspars can form clay minerals through chemical weathering..[10]


Feldspar output in 2005. Click the image for the details.

In 2005, Italy was the top producer of feldspar with almost one-fifth world share followed by Turkey, China and Thailand, reports theInternational Monetary Fund.



For other uses, see Hematite (disambiguation).

Hematite (blood ore) from the US state ofMichigan (unknown scale)
Category Oxide mineral
Chemical formula iron(III) oxide, Fe2O3, α-Fe2O3
Color Metallic gray to earthy red tones
Crystal habit Tabular to thick crystals
Crystal system Hexagonal (rhombohedral)
Cleavage None
Fracture Uneven to sub-conchoidal
Mohs Scalehardness 5.5 – 6.5
Luster Metallic to splendent
Streak Bright red to dark red
Specific gravity 4.9 – 5.3
Refractive index Opaque
Pleochroism None
References [1][2]

Hematite in SEM, magnification 100x

Close-up of hematitic Banded Iron Formation specimen from Upper Michigan. Scale bar is 5.0 mm.

Hematitealso spelled as hæmatite, is the mineral form of Iron(III) oxide (Fe2O3), one of several iron oxides. Hematite crystallizes in the rhombohedral system, and it has the samecrystal structure as ilmenite and corundum. Hematite and ilmenite form a completesolid solution at temperatures above 950°C.

Hematite is a mineral, colored black to steel or silver-gray, brown to reddish brown, or red. It ismined as the main ore of iron. Varieties include kidney oremartite (pseudomorphs aftermagnetite), iron rose and specularite (specular hematite). While the forms of hematite vary, they all have a rust-red streak. Hematite is harder than pure iron, but much more brittle.Maghemite is a hematite- and magnetite-related oxide mineral.

Huge deposits of hematite are found in banded iron formations. Grey hematite is typically found in places where there has been standing water or mineral hot springs, such as those inYellowstone National Park in the United States. The mineral can precipitateout of water and collect in layers at the bottom of a lake, spring, or other standing water.. Hematite can also occur without water, however, usually as the result of volcanic activity.

Clay-sized hematite crystals can also occur as a secondary mineral formed by weatheringprocesses in soil, and along with other iron oxides or oxyhydroxides such as goethite, is responsible for the red color of many tropical, ancient, or otherwise highly weathered soils.

Good specimens of hematite come from EnglandMexicoBrazilAustraliaUnited States andCanada.

Etymology and history

Main article: Ochre

Ancient Egyptian cylindrical seal (left) made from hematite with corresponding impression (right), approximately 14th century BC

The name hematite is derived from the Greek word for blood (haima ἁιμα) because hematite can be red, as in rouge, a powdered form of hematite. The color of hematite lends it well in use as a pigment.

Ochre is a clay that is colored by varying amounts of hematite, varying between 20% and 70%[3]Red ochre contains unhydrated hematite, whereas yellow ochre contains hydratedhematite (Fe2O3 • H2O).. The principal use of ochre is for tinting with a permanent color[3].

The red chalk winning of this mineral was one of the earliest in history of mankind. The powdery mineral was first used 164,000 years ago by the Pinnacle-Point man obviously for social differentiation[4]. Hematite residues are also found in old graveyards from 80,000 years ago. Near Rydno in Poland and Lovas in Hungary, palaeolitic red chalk mines have been found that are from 5000 BC, belonging to the Linear Pottery culture at the Upper Rhine.

Rich deposits of hematite have been found on the island of Elba that have been mined till the time of the Etruscans.

Ancient Egyptian booby trap

In 2001, Egyptian government archaeologist Zahi Hawass was the first to enter a previously undisturbed tomb, believed to be that of an ancient regional mayor, in the Bahariya Oasisbelow the town of Bawiti. Upon entering the burial chamber, Hawass discovered abooby trapconsisting of 8 inches of finely powdered hematite dust covering the floor and sarcophagus.[5]When disturbed by a tomb robber, the sharp, metallic dust was intended to become airborne and irritate the skin, eyes and mucous membranes, eventually causing lethal siderosis if exposed for long enough. The archaeological team was forced to retreat and don full body suits and respirators in order to confirm the identity of the mummy. Hawass cites the ancient Egyptians’ experience with powdered hematite as a paint pigment as proof that they were aware of its irritating properties.[6]


Hematite carving, 5 cm (2 in) long.

Hematite’s popularity in jewelry was at its highest in Europe during the Victorian era, and has since seen a strong resurgence inNorth America, especially in the western United States.. Due to it delicate nature, the mineral is found only in precious jewelry. Extreme care should be taken in handling hematite items due to the material’s susceptibility to irreversible damage.

It is also used in art such as intaglios where it is used for making hollow portraits.


crystal structure of hematite

Hematite is an antiferromagnetic material below the Morin transition at 250 K, and a canted antiferromagnet or weakly ferromagneticabove the Morin transition and below its Néel temperature at 948K, above which it is paramagnetic.

The magnetic structure of a-hematite was the subject of considerable discussion and debate in the 1950s because it appeared to be ferromagnetic with a Curie temperature of around 1000 K, but with an extremely tiny moment (0.002 µB). Adding to the surprise was a transition with a decrease in temperature at around 260 K to a phase with no net magnetic moment. It was shown that the system is essentially antiferromagnetic but that the low symmetry of the cation sites allows spin–orbit coupling to cause canting of the moments when they are in the plane perpendicular to the c axis. The disappearance of the moment with a decrease in temperature at 260 K is caused by a change in the anisotropy which causes the moments to align along the c axis. In this configuration, spin canting does not reduce the energy.[7][8]

Hematite is part of a complex solid solution oxyhydroxide system having various degrees of water, hydroxyl group, and vacancy substitutions that affect the mineral’s magnetic and crystal chemical properties.[9] Two other end-members are referred to as protohematite and hydrohematite.

Iron from mine tailings

Hematite is present in the waste tailings of iron mines. A recently developed process,magnetation, uses huge magnets to glean waste hematite from old mine tailings inMinnesota‘s vast Mesabi Range iron district.[10]

Hematite on Mars

Image mosaic from the Mars Exploration Rover Microscopic Imager shows Hematitespherules partly embedded in rock at the Opportunity landing site. (Scale: image is approximately 5 cm (2 in) across)

The spectral signature of hematite was seen on the planet Mars by the infrared spectrometeron the NASA Mars Global Surveyor(“MGS”) and 2001 Mars Odyssey spacecraft in orbit around Mars.[11] The mineral was seen in abundance at two sites [12] on the planet, the Terra Meridiani site, near the Martian equator at 0° longitude, and the second site Aram Chaos near the Valles Marineris.[13] Several other sites also showed hematite, e.g., Aureum Chaos.[14]Because terrestrial hematite is typically a mineral formed in aqueous environments, or by aqueous alteration, this detection was scientifically interesting enough that the second of the two Mars Exploration Rovers was targeted to a site in the Terra Meridiani region designatedMeridiani Planum. In-situ investigations by the Opportunity rover showed a significant amount of hematite, much of it in the form of small spherules that were informally tagged by the science team “blueberries”. Analysis indicates that these spherules are apparentlyconcretions formed from a water solution.

Posted by Ajitchandra vijayji at  1:33 AM 0 comments



This article is about the mineral named zoisite. For the Sailor Moon character, see Shitennou.

Anyolite (left) & tanzanite
Category Sorosilicate – epidote group
Chemical formula Ca2Al3(SiO4)(Si2O7)O(OH)
Strunz classification VIII/C.23-100
Dana classification 58.2.1b.1
Color White, gray, greenish brown, greenish gray, pink, blue, purple
Crystal habit Crystals flattened in an acicular manner, may be fibrously curved and striated. Massive to columnar
Crystal system Orthorhombic – Dipyramidal
Cleavage Perfect {010} imperfect {100}
Fracture Uneven to conchoidal
Mohs Scalehardness 6 to 7
Luster Vitreous, pearly on cleavage surfaces
Streak White or colorless
Diaphaneity Transparent to translucent
Specific gravity 3.10-3.36
Optical properties biaxial positive
Refractive index nα = 1..696 – 1.700 nβ = 1.696 – 1.702 nγ = 1.702 – 1.718
Birefringence 0.006-0.018
Pleochroism X = pale pink to red-violet; Y = nearly colorless to bright pink or deep blue; Z = pale yellow to yellow-green
References [1][2][3]
Major varieties
Tanzanite Gem-quality zoisite, blue-purple
Thulite Pink

Zoisite is a calcium aluminium hydroxy sorosilicate belonging to the epidote group ofminerals. Its chemical formula isCa2Al3(SiO4)(Si2O7)O(OH). Zoisite is named after theSlovene scientist Baron Sigmund Zois von Edelstein (Žiga Zois), who realized that this was an unknown mineral when it was brought to him by the mineral dealer Simon Prešern, who had discovered it in theSaualpe mountains (Svinška planina) of Carinthia in 1805. Zoisite was first known as saualpite, after its type locality.

Zoisite occurs as prismaticorthorhombic (2/m 2/m 2/m) crystals or in massive form, being found in metamorphic and pegmatiticrock. Zoisite may be blue to violet, green, brown, pink, yellow, gray, or colorless. It has a vitreous luster and a conchoidal to unevenfracture. When euhedral, zoisite crystals are striated parallel to the principal axis (c-axis). Also parallel to the principal axis is one direction of perfect cleavage. Zoisite is somewhat higher than 6 inhardness and its specific gravity is between 3.10 – 3.38, depending on the variety. Zoisite streaks white and is said to be brittle. Clinozoisite is a more common monoclinic polymorph of zoisite.

Transparent material is fashioned into gemstones while translucent-to-opaque material is usually carved. A metamorphic rock known as anyolite consists of green zoisite with blacktschermakite and ruby crystals.[4][5]

Sources of zoisite include Tanzania (tanzanite), Kenya (anyolite), Norway (thulite),SwitzerlandAustriaIndiaPakistan, andWashington in the USA.



This article is about the gemstone. For the Sailor Moon character, see Nephrite (character).
Not to be confused with Nephritis.

Category Mineral
Chemical formula Ca2(Mg,Fe)5Si8O22(OH)2[1]
Color Translucent to opaque and often mottled. Light to dark green, yellow to brown, white, gray, black.[1]
Crystal habit massive[1]
Crystal system monoclinic[1]
Fracture splintery to granular[1]
Mohs Scalehardness 6 – 6.5[1]
Luster dull[1]
Specific gravity 2.95 (+.15, -.05)[1]
Polish luster vitreous to greasy[1]
Optical properties Double refractive with anomalous aggregate reaction[1]
Refractive index 1.606 – 1.632 (+.009, -.006)[1]
Birefringence usually not detectable[1]
Pleochroism none[1]
Ultravioletfluorescence inert[1]
Absorption spectra Vague line may be present at 500 nm, but rarely any lines. Rarely, in stones of exceptional gem quality, vague lines in the red part of the spectrum may be seen.[1]

Nephrite is a variety of the calcium and magnesium-rich amphibole mineral actinolite(aggregates of which also make up one form ofasbestos). The chemical formula for nephrite isCa2(Mg,Fe)5Si8O22(OH)2.[1] It is one of two different mineral species called jade. The other mineral species known as jade is jadeite, which is a variety of pyroxene. While nephrite jade possess mainly grays and greens (and occasionally yellows, browns or whites), Jadeite jade, which is rarer, can also contain blacks, reds, pinks and violets. Nephrite jade is an ornamental stone, used in carvingsbeads, or cabochon cut gemstones.

The name nephrite is derived from lapis nephriticus, which means ‘kidney stone’ and is the Latin version of the Spanish piedra de ijada.[2] Accordingly, nephrite jade was once believed to be a cure for kidney stones.

Nephrite can be found in a translucent white to very light yellow form which is known in China as mutton fat jade,[1] in an opaque white to very light brown or gray which is known aschicken bone jade,[1] as well as in a variety of green colours. Canada is the principal source of modern lapidary nephrite. Nephrite jade was used mostly in pre-1800 China as well as in New Zealand, the Pacific Coast and Atlantic Coasts of North America, Neolithic Europe, and southeast Asia.


Prehistoric and historic China

During Neolithic times, the key known sources of nephrite jade in China for utilitarian and ceremonial jade items were the now depleted deposits in the Ningshao area in the Yangtze River Delta (Liangzhu culture 3400–2250 BC) and in an area of the Liaoning province in Inner Mongolia (Hongshan culture 4700–2200 BC). Jade was used to create many utilitarian and ceremonial objects, ranging from indoor decorative items to jade burial suits. Jade was considered the “imperial gem”. From about the earliest Chinese dynasties until present, the jade deposits in most use were from the region of Khotan in the Western Chinese province ofXinjiang(jade deposits from other areas of China, such as LantianShaanxi, were also in great demand). There, white and greenish nephrite jade is found in small quarries and as pebbles and boulders in the rivers flowing from the Kuen-Lun mountain range northward into theTakla-Makan desert area. River jade collection was concentrated in the Yarkand, the White Jade (Yurungkash) and Black Jade (Karakash) Rivers. From the Kingdom of Khotan, on the southern leg of the Silk Road, yearly tribute payments consisting of the most precious white jade were made to the Chinese imperial court and there transformed into objets d’art by skilled artisans, as jade was considered more valuable than gold or silver.


Nephrite jade in New Zealand is known as pounamu in the Māori language, and is highly valued, playing an important role in Māoriculture. It is considered a taonga, or treasure, and therefore protected under the Treaty of Waitangi, and the exploitation of it is restricted and closely monitored. The South Island of New Zealand is Te Wai Pounamu in Māori — “The [land of] Greenstone Water” — because that is where it occurs.


Weapons and ornaments were made of it; in particular the mere (short club), and the hei-tiki(neck pendant). These were believed to have their own mana, were handed down as valuable heirlooms, and often given as gifts to seal important agreements. It was also used for a range of tools such as adzes, as Māori had no metal tools.

In New Zealand English its normal name is “greenstone”. Jade jewellery in Māori designs is widely popular with locals of all races, and with tourists – although much of the jade itself is now imported from British Columbia and elsewhere.

Other names

Besides the terms already mentioned, nephrite has the following synonyms and varieties:aoteaaxe-stoneB.C. jadebeilstein,kidney stonelapis nephriticusnephritnephritaNew Zealand greenstone,[1] New Zealand jade,[1] spinach jade (dark grayish green),[1] and talcum nephriticusTomb jade or grave jade are names given to ancient burial nephrite pieces that have a brown or chalky white texture as a surface treatment.[1]



“Nephrite jade” redirects here. You may be looking for Nephrite.
This article is about the gemstone. For other uses, see Jade (disambiguation).

A selection of antique, hand craftedChinesejade (jadeite) buttons.

Unworked jade

Jade is an ornamental stone. The term jade is applied to two different metamorphic rocks that are made up of different silicate minerals:

  • Nephrite jade, consists of a microcrystaline interlocking fibrous matrix of the calcium, magnesium-iron rich amphibole mineral series tremolite (calcium-magnesium)-ferroactinolite (calcium-magnesium-iron). The middle member of this series with an intermediate composition is calledactinolite (the silky fibrous mineral form is one form of asbestos). The higher the iron content the greener the colour.
  • Jadeitite, a rock consisting almost entirely of jadeite, a sodium- and aluminium-rich pyroxene. The gem form of the mineral is a microcrystaline interlocking crystal matrix.

The English word jade is derived from the Spanish term piedra de ijada (first recorded in 1565) or “loin stone”, from its reputed efficacy in curing ailments of the loins and kidneysNephrite is derived from lapis nephriticus, the Latin version of the Spanish piedra de ijada.[1]

Nephrite and jadeite were used by people from the prehistoric for similar purposes. Jadeite has about the same hardness as quartz, while nephrite is somewhat softer. Both nephrite and jadeite are tough, but nephrite is tougher than jadeite. They can be delicately shaped. Thus it was not until the 19th century that a French mineralogist determined that “jade” was in fact two different materials. The trade name jadite is sometimes applied to translucent or opaque green glass.

Among the earliest known jade artifacts excavated from prehistoric sites are simple ornaments with bead, button, and tubular shapes.[2] Additionally, jade was used for axe heads, knives, and other weapons. As metal-working technologies became available, the beauty of jade made it valuable for ornaments and decorative objects. Jadeite measures between 6.5 and 7.0 Mohs hardness, and Nephrite between 5.5 and 6.0,[3] so it can be worked with quartz or garnet sand, and polished with bamboo or even ground jade.

Nephrite can be found in a creamy white form (known in China as “mutton fat” jade) as well as in a variety of green colours, whereas jadeite shows more colour variations, including blue, lavender-mauve, pink, and emerald-green colours. Of the two, jadeite is rarer, documented in fewer than 12 places worldwide. Translucent emerald-green jadeite is the most prized variety, both today and historically. As “quetzal” jade, bright green jadeitite from Guatemala was treasured by Mesoamerican cultures, and as “kingfisher” jade, vivid green rocks from Burma became the preferred stone of post-1800 Chinese imperial scholars and rulers. Burma (Myanmar) and Guatemala are the principal sources of modern gem jadeitite, and Canada of modern lapidary nephrite. Nephrite jade was used mostly in pre-1800 China as well as in New Zealand, the Pacific Coast and Atlantic Coasts of North America, Neolithic Europe, and south-east Asia.. In addition to Mesoamerica, jadeite was used by Neolithic Japanese and European cultures.

Jade is the official gemstone of British Columbia, where it is found in large deposits in the Lillooet andCassiar regions. It is also the official gemstone of the state of Alaska, found particularly in the Kobuk area. A two-ton block of jade sits outside the Anchorage Visitor’s Center in downtown Anchorage, Alaska, mined from near Kobuk and donated to the city as a showpiece. Jade is also the state gemstone of the State ofWyoming.[citations needed]

The 2008 Summer Olympic medals have a ring of jade in them.


Prehistoric and Historic China

Main article: Chinese jade

During Neolithic times, the key known sources of nephrite jade in China for utilitarian and ceremonial jade items were the now depleted deposits in the Ningshao area in the Yangtze River Delta (Liangzhu culture3400–2250 BC) and in an area of the Liaoning province and Inner Mongolia (Hongshan culture 4700–2200 BC).[4] As early as 6000 BC Dushan Jade has been mined.. In the Yin Ruins of Shang Dynasty (1600 BC to 1050 BC) in Anyang, Dushan Jade ornaments was unearthed in the tomb of the Shang kings. Jade was used to create many utilitarian and ceremonial objects, ranging from indoor decorative items to jade burial suits. Jade was considered the “imperial gem”. From about the earliest Chinese dynasties until present, the jade deposits in most use were not only from the region of Khotan in the Western Chinese province ofXinjiang but also from other parts of China, such as Lantian, Shaanxi. There, white and greenish nephrite jade is found in small quarries and as pebbles and boulders in the rivers flowing from the Kuen-Lun mountain range northward into the Takla-Makan desert area. River jade collection was concentrated in theYarkand, the White Jade (Yurungkash) and Black Jade (Karakash) Rivers. From the Kingdom of Khotan, on the southern leg of the Silk Road, yearly tribute payments consisting of the most precious white jade were made to the Chinese Imperial court and there transformed intoobjets d’art by skilled artisans as jade was considered more valuable than gold or silver. Jade became a favorite material for the crafting of Chinese scholars objects, such as rests for calligraphy brushes, as well as the mouthpieces of some opium pipes, due to the belief that breathing through jade would bestow longevity upon smokers who used such a pipe.[5]

Jadeite, with its bright emerald-green, pink, lavender, orange and brown colours was imported from Burmato China only after about 1800. The vivid green variety became known as Feicui (翡翠) or Kingfisher (feathers) Jade. It quickly replaced nephrite as the imperial variety of jade.

In the long history of the art and culture of the enormous Chinese empire, jade has always had a very special significance, roughly comparable with that of gold and diamonds in the West. Jade was used not only for the finest objects and cult figures, but also in grave furnishings for high-ranking members of the imperial family.

Prehistoric and Early Historic Korea

Korean National Treasure No. 191, a gold crown with comma-shaped jades, was excavated from theHeavenly Horse Tomb of Sillaand dates to the 5th century AD.

The use of jade and other greenstone was a long-term tradition in Korea (c. 850 BC – AD 668). Jade is found in small numbers of pit-houses and burials. The craft production of small comma-shaped and tubular ‘jades’ using materials such as jade, microclinejasper, etc in southern Korea originates from the MiddleMumun Pottery Period (c. 850–550 BC).[6] Comma-shaped jades are found on some of the gold crowns ofSilla royalty (c. AD 300/400–668) and sumptuous elite burials of the Korean Three Kingdoms. After the state of Silla united the Korean Peninsula in AD 668, the widespread popularisation of death rituals related to Buddhism resulted in the decline of the use of jade in burials as prestige mortuary goods.


Nephrite jade in New Zealand is known as pounamu in the Māori language, playing an important role inMāori culture. It is considered a taonga, or treasure, and therefore protected under the Treaty of Waitangi, and the exploitation of it is restricted and closely monitored. It is found only in the South Island of New Zealand, known as Te Wai Pounamu in Māori — “The [land of] Greenstone Water”, or Te Wahi Pounamu— “The Place of Greenstone”.

Tools, weapons and ornaments were made of it; in particular adzes, the ‘mere‘ (short club), and the Hei-tiki(neck pendant). These were believed to have their own mana, handed down as valuable heirlooms, and often given as gifts to seal important agreements.

One name used for nephrite jade in New Zealand English is “greenstone.” While widely used to describe the material used for jewellery items made for the tourist trade, it is a misnomer and simply engenders confusion. The stone should be correctly referred to as “nephrite” or “nephrite jade”. Nephrite jewellery of Maori design is widely popular with locals and tourists, although some of the jade used for these is now imported from British Columbia and elsewhere.[7]


Jadeite Pectoral from theMayan Classic period. (195 mm/7.7 in high)

Jade pendant, found in a tomb in TikalGuatemala

Jade was a rare and valued material in pre-Columbian Mesoamerica. The only source from which the various indigenous cultures, such as theOlmec and Maya, for example, could obtain jade was located in theMotagua River valley in Guatemala. Jade was largely an elite good, and was usually carved in a variety ways, whether serving as a medium upon which hieroglyphs were inscribed, or shaped into symbolic figurines.. Generally, the material was highly symbolic, and it was often employed in the performance of ideological practices and rituals.

Today, Guatemala produces jadeite in a variety of colours, ranging from soft translucent lilac, blue, green, yellow, and black. It is also the source of new colours, including “rainbow jade” and the unique “Galactic Gold,” a black jadeite with natural incrustations of gold, silver and platinum.[8]

Prehistoric and Historic India

The Jainist temple of Kolanpak in the Nalgonda districtAndhra Pradesh,India is home to a 5-foot (1.5 m) high sculpture of Mahavira that is carved entirely out of jade. The is the largest sculpture made from a single jade rock in the world.

Other names

Besides the terms already mentioned, jadeite and nephrite are sometimes referred to by the following:


  • Agate verdâtre
  • Feitsui
  • Jadeit
  • Jadeita
  • Natronjadeit
  • Yunnan Jade
  • Yu-stone


  • Aotea
  • Axe-stone
  • B.C. Jade
  • Beilstein
  • British Columbian Jade
  • Canadian Jade
  • Dushan Jade
  • Nanyang Jade
  • Du Jade
  • Henan Yu
  • Grave Jade
  • Kidney Stone
  • Lapis Nephriticus
  • Nephrit
  • Nephrita
  • Nephrite (of Werner)
  • New Zealand Greenstone
  • New Zealand Jade
  • Siberian Jade
  • Sinkiang jade
  • Spinach Jade
  • Talcum Nephriticus
  • Tomb Jade

Faux jade

Many minerals are sold as jade. Some of these are: serpentine (also bowenite), carnelianaventurine quartzglassgrossularite,Vesuvianitesoapstone (and other steatites such as shoushan stone) and recently, Australian chrysoprase. “Korean jade,” “Suzhou jade,” “Styrian jade,” “Olive jade”, and “New jade” are all really serpentine; “Transvaal jade” or “African jade” is grossularite; “Peace jade” is a mixture of serpentine, stichtite, and quartz; “Mountain jade” is dyed dolomite marble.

In almost all dictionaries, the Chinese character ‘yù’ (玉) is translated into English as ‘jade’. However, this frequently leads to misunderstanding: Chinese, Koreans, and Westerners alike generally fail to appreciate that the cultural concept of ‘jade’ is considerably broader in China and Korea than in the West. A more accurate translation for this character on its own would be ‘precious/ornamental rock’. It is seldom, if ever, used on its own to denote ‘true’ jade in Mandarin Chinese; for example, one would normally refer to ‘ying yu’ (硬玉, ‘hard jade’) for jadeite, or ‘ruan yu’ (軟玉, ‘soft jade’) for nephrite. The Chinese names for many ornamental non-jade rocks also incorporate the character ‘yù’, and it is widely understood by native speakers that such stones are not, in fact, true precious nephrite or jadeite. Even so, for commercial reasons, the names of such stones may well still be translated into English as ‘jade’, and this practice continues to confuse the unwary.


Jade may be enhanced (sometimes called “stabilized”). There are three main methods, sometimes referred to as the ABC Treatment System:

  • Type A jadeite has not been treated in any way except surface waxing.
  • Type B treatment involves exposing a promising but stained piece of jadeite to chemical bleaches and/or acids and impregnating it with a clear polymer resin. This results in a significant improvement of transparency and colour of the material. Currently, infrared spectroscopy is the most accurate test for the detection of polymer in jadeite.
  • Type C jade has been artificially stained or dyed. The red colour of Red jade can be enhanced with heat. The effects are somewhat uncontrollable and may result in a dull brown. In any case, translucency is usually lost.
  • B+C jade is a combination of B and C: it has been both artificially dyed AND impregnated.
  • Type D jade refers to a composite stone such as a doublet comprising a jade top with a plastic backing.[9]

Gallery of Chinese jades

Jade dragon ring, Shang Dynasty (1700 BC-1150 BC)

Jade dragon, Warring States (403 BC-221 BC)

A jade Bi with dragons,Warring States(403 BC-221 BC)

Jade coiled serpent, Han Dynasty (202 BC-220 AD)

Jade-dragon belt clasp, Liu Song Dynasty(420-479AD)

Jade dragon, Tang Dynasty (618-907 AD)

Belt plaque with dragon,Yuan Dynasty(1279-1368AD)

Belt plaque with dragon,Ming Dynasty(1368-1644AD)



This article is about semi-precious stone. For other uses, see Agate (disambiguation).

Moss agate pebble, 2.5 cm (1 inch) long
Category Quartz variety
Chemical formula Silica, SiO2
Color White to grey, light blue, orange to red, black.
Crystal habit Cryptocrystalline silica
Crystal system Rhombohedral Microcrystalline
Cleavage None
Fracture Conchoidal with very sharp edges.
Mohs Scalehardness 7
Luster Waxy
Streak White
Specific gravity 2.58-2.64
Refractive index 1.530-1.540
Birefringence up to +0.004 (B-G)
Pleochroism Absent

Agate (pronounced /ˈæɡət/) is a microcrystalline variety of quartz (silica), chiefly chalcedony, characterised by its fineness of grain and brightness of color. Although agates may be found in various kinds of rock, they are classically associated with volcanic rocks but can be common in certainmetamorphic rocks.[1]

Colorful agates and other chalcedonies were obtained over 3,000 years ago from the Achates River, now called Dirillo, in Sicily.[2]

The stone was given its name by Theophrastus, a Greek philosopher and naturalist, who discovered the stone along the shore line of the river Achates (GreekΑχάτης) sometime between the 4th and 3rd centuries BC.[3] The agate has been recovered at a number of ancient sites, indicating its widespread use in the ancient world; for example, archaeological recovery at the Knossos site on Creteillustrates its role in Bronze Age Minoanculture.[4]

Formation and characteristics

Most agates occur as nodules in volcanic rocks or ancient lavas where they represent cavities originally produced by the disengagement of volatilesin the molten mass which were then filled, wholly or partially, by siliceous matter deposited in regular layers upon the walls. Such agates, when cut transversely, exhibit a succession of parallel lines, often of extreme tenuity, giving a banded appearance to the section. Such stones are known as banded agate, riband agate and striped agate.

In the formation of an ordinary agate, it is probable that waters containing silica in solution—derived, perhaps, from the decomposition of some of the silicates in the lava itself—percolated through the rock and deposited a siliceous coating on the interior of the vapour-vesicles. Variations in the character of the solution or in the conditions of deposition may cause a corresponding variation in the successive layers, so that bands of chalcedony often alternate with layers of crystalline quartz. Several vapour-vesicles may unite while the rock is still viscous, and thus form a large cavity which may become the home of an agate of exceptional size; thus a Brazilian geode lined with amethyst and weighing 67 tons was exhibited at theDusseldorf Exhibition of 1902. Perhaps the most comprehensive review of agate chemistry is a recent text by Moxon cited below.

The first deposit on the wall of a cavity, forming the “skin” of the agate, is generally a dark greenish mineral substance, likeceladonitedelessite or “green earth“, which are rich in iron probably derived from the decomposition of the augite in the enclosing volcanic rock. This green silicate may give rise by alteration to a brown iron oxide (limonite), producing a rusty appearance on the outside of the agate-nodule. The outer surface of an agate, freed from its matrix, is often pitted and rough, apparently in consequence of the removal of the original coating. The first layer spread over the wall of the cavity has been called the “priming”, and upon this base zeolitic minerals may be deposited.

Many agates are hollow, since deposition has not proceeded far enough to fill the cavity, and in such cases the last deposit commonly consists of quartz, often amethyst, having the apices of the crystals directed towards the free space so as to form a crystal-lined cavity, or geode.

On the disintegration of the matrix in which the agates are embedded, they are set free. The agates are extremely resistant to weathering and remain as nodules in the soil or are deposited as gravel in streams and shorelines.

Types of agate

Banded agate (agate-like onyx). The specimen is 2.5 cm (1 inch) wide.

Agatized Coral

Montana moss agate

“Turritella agate” (Elimia tenera) from Green River Formation, Wyoming

Faceted Botswana agate

A Mexican agate, showing only a single eye, has received the name of cyclops agate. Included matter of a green, golden, red, black or other color or combinations embedded in the chalcedony and disposed in filaments and other forms suggestive of vegetable growth, gives rise to dendritic or moss agateDendritic agates have fern like patterns in them formed due to the presence of manganese and iron oxides. Other types of included matter deposited during agate-building include sagenitic growths (radial mineral crystals) and chunks of entrapped detritus (such as sand, ash, or mud). Occasionally agate fills a void left by decomposed vegetative material such as a tree limb or root and is called limb cast agate due to its appearance.

Turritella agate is formed from silicified fossil Turritella shells. Turritella are spiral marine gastropods having elongated, spiral shells composed of many whorls. Similarly, coralpetrified wood and other organic remains or porous rocks can also become agatized. Agatized coral is often referred to as Petoskey stone or agate.

Greek agate is a name given to pale white to tan colored agate found in Sicily back to 400 B.C. The Greeks used it for making jewelry and beads. Today any agate of this color from Sicily, once an ancient Greek colony, is called Greek agate. Yet the stone had been around centuries before that and was known to both the Sumerians and the Egyptians, who used the gem for decoration and religious ceremony.

Another type of agate is Brazilian agate, which is found as sizable geodes of layered nodules. These occur in brownish tones interlayered with white and gray. Quartz forms within these nodules, creating a striking specimen when cut opposite the layered growth axis. It is often dyed in various colors for ornamental purposes.

Certain stones, when examined in thin sections by transmitted light, show a diffraction spectrum due to the extreme delicacy of the successive bands, whence they are termed rainbow agates. Often agate coexists with layers or masses of opal, jasper or crystalline quartz due to ambient variations during the formation process.

Other forms of agate include carnelian agate (usually exhibiting reddish hues), Botswana agate, Ellensburg blue agate, blue lace agate, plume agates, tube agate (with visible flow channels), fortification agate (which exhibit little or no layered structure), fire agate (which seems to glow internally like an opal) and Mexican crazy-lace agate (which exhibits an often brightly colored, complex banded pattern) also called Rodeo Agate and Rosetta Stone depending on who owned the mine at the time.

Uses in industry and art

Industry uses agates chiefly to make ornaments such as pins, brooches, paper knives, inkstands, marbles and seals. Because of its hardness and ability to resist acids, agate is used to make mortars and pestles to crush and mix chemicals. Because of the high polish possible with agate it has been used for centuries for leather burnishing tools. Idar-Oberstein was one of the centers which made use of agate on an industrial scale. Where in the beginning locally found agates were used to make all types of objects for the European market, this became a globalized business around the turn of the 20th century: Idar-Oberstein imported large quantities of agate from Brazil, as ship’s ballast. Making using of a variety of proprietary chemical processes, they produced colored beads that were sold around the globe.[5] Agates have long been used in arts and crafts. The sanctuary of a Presbyterian church in Yachats, Oregon, has six windows with panes made of agates collected from the local beaches.



This article is about the mineral. For the fictional character, see Trolls (Discworld).


Chrysoprase or chrysophrase is a gemstone variety of chalcedony (a cryptocrystalline form of silica) that contains small quantities of nickel. Its color is normally apple-green, but varies to deep green. The darker varieties of chrysoprase are also referred to asprase. (However, the term prase is also used to describe chlorite-included quartz, and to a certain extent is a color-descriptor, rather than a rigorously defined mineral variety.)

Chrysoprase is cryptocrystalline, which means that it is composed of crystals so fine that they cannot be seen as distinct particles under normal magnification. This sets it apart from rock crystal, amethystcitrine, and the other varieties of crystalline quartz which are basically transparent and formed from easily recognized six-sided crystals. Other members of the cryptocrystalline silica family include agatecarnelian, and onyx. Unlike many non-transparent silica minerals, it is the color of chrysoprase, rather than any pattern of markings, that makes it desirable. The word chrysoprase comes from the Greek chrysos meaning ‘gold’ and prason, meaning ‘leek’.

Unlike emerald which owes its green color to the presence of chromium, the color of chrysoprase is due to trace amounts of nickelcompounds in form of very small inclusions. The nickel reportedly occurs as different silicates, like kerolite or pimelite (not NiO mineral, bunsenite, as was reported before). Chrysoprase results from the deep weathering orlateritization of nickeliferousserpentinites or other ultramafic ophiolite rocks. In the Australian deposits, chrysoprase occurs as veins and nodules with browngoethite and other iron oxidesin the magnesite-rich saprolite below an iron and silica cap.

As with all forms of chalcedony, chrysoprase has a hardness of 6 – 7 on the Mohs hardness scale and a conchoidal fracture like flint.

The best known sources of chrysoprase are QueenslandWestern AustraliaGermany,PolandRussiaArizonaCalifornia, andBrazil. The chrysoprase and Ni silicate ore deposit in Szklary, Lower Silesia, Poland, was probably the biggest European chrysoprase occurrence and possibly also the biggest in the world.

A very similar mineral to chrysoprase is chrome chalcedony, in which the color is provided bychromium rather than nickel.

Posted by Ajitchandra vijayji at  1:17 AM 0 comments




A cut and polished Chalcedony geode
Category Oxide mineral
Chemical formula Silica (silicon dioxide, SiO2)
Molar mass 60 g / mol
Color Various
Crystal system Trigonal
Cleavage Absent
Fracture Uneven, splintery, conchoidal
Mohs Scalehardness 6 – 7
Luster Waxy, vitreous, dull, greasy, silky
Streak White
Diaphaneity Translucent
Specific gravity 2.59 – 2.61
References [1]

Chalcedony is a cryptocrystalline form of silica, composed of very fine intergrowths of the minerals quartz and moganite[2]. These are both silica minerals, but they differ in that quartz has a trigonal crystal structure, whilst moganite is monoclinic.

Chalcedony has a waxy luster, and may be semitransparent or translucent. It can assume a wide range of colors, but those most commonly seen are white to gray, grayish-blue or a shade of brown ranging from pale to nearly black.


Chalcedony occurs in a wide range of varieties. Many semi-precious gemstones are in fact forms of chalcedony. The more notable varieties of chalcedony are as follows:



Agate is a variety of chalcedony with multi-colored concentric banding.



Carnelian (also spelled cornelian) is a clear-to-translucent reddish-brown variety of chalcedony. Its hue may vary from a pale orange, to an intense almost-black coloration. Similar to carnelian is sard, which is brown rather than red.



Chrysoprase (also spelled chrysophrase) is a green variety of chalcedony, which has been colored by nickel oxide. (The darker varieties of chrysoprase are also referred to as prase. However, the term prase is also used to describe green quartz, and to a certain extent is a color-descriptor, rather than a rigorously defined mineral variety.)


Heliotrope, or bloodstone

Heliotrope is a green variety of chalcedony, containing red inclusions of iron oxide. These inclusions resemble drops of blood, giving heliotrope its alternative name of bloodstone. A similar variety, in which the spots are yellow instead of red is known as plasma.

Moss agate

Moss agate

Moss agate (also known as tree agate or mocha stone) contains green filament-like inclusions, giving it the superficial appearance of moss or blue cheese. It is not a true form of agate, as it lacks agate’s defining feature of concentric banding.



Mtorolite is a green variety of chalcedony, which has been colored by chromium. It is principally found in Zimbabwe.


Several onyx forms

Onyx is a variant of agate with black and white banding. Similarly, agate with brown and white banding is known as sardonyx.


Chalcedony cameo ofTitushead, 2nd Century AD

As early as the Bronze Age chalcedony was in use in the Mediterranean region; for example, on Minoan Crete at the Palace ofKnossos, chalcedony seals have been recovered dating to circa 1800 BC.[3] People living along the Central Asian trade routes used various forms of chalcedony, including carnelian, to carve intaglios, ring bezels (the upper faceted portion of a gem projecting from the ring setting), and beads that show strong Graeco-Roman influence. Fine examples of first century objects made from chalcedony, possibly Kushan, were found in recent years at Tillya-tepe in north-western Afghanistan[4] Hot wax would not stick to it so it was often used to make seal impressions. The term chalcedony is derived from the name of the ancient Greek town Chalkedon in Asia Minor, in modern English usually spelledChalcedon, today the Kadıköy district of Istanbul.

Chalcedony knife, AD 1000-1200



Chalcedony was once regarded to be a fibrous variety of cryptocrystalline quartz [5]. More recently however, it has been shown to also contain a monoclinic polymorph of quartz, known as moganite[2]. The fraction, by mass, of moganite within a typical chalcedony sample may vary from less than 5% to over 20%[6]. The existence of moganite was once regarded as dubious, but it is now officially recognised by the International Mineralogical Association[7][8].


Chalcedony is more soluble than quartz under low-temperature conditions, despite the two minerals being chemically identical. This is thought to be because chalcedony is extremely finely grained (cryptocrystalline), and so has a very high surface area to volume ratio.[citation needed] It has also been suggested that the higher solubility is due to the moganite component [6].

Solubility of quartz and chalcedony in pure water

This table gives equilibrium concentrations of total dissolved silicon as calculated by PHREEQC using the llnl.dat database.

Temperature Quartz Solubility (mg/L) Chalcedony Solubility (mg/L)
0.01°C 0.68 1.34
25.0°C 2.64 4.92
50.0°C 6.95 12.35
75.0°C 14.21 24.23
100.0°C 24.59 40.44



For other uses, see Amethyst (disambiguation).
Category Mineral variety
Chemical formula Silica (silicon dioxide, SiO2)
Color Violet
Crystal habit 6-sided prism ending in 6-sided pyramid (typical)
Crystal system rhombohedral class 32
Twinning Dauphine law, Brazil law, and Japan law
Cleavage None
Fracture Conchoidal
Mohs Scalehardness 7–lower in impure varieties
Luster Vitreous/glossy
Streak White
Diaphaneity Transparent to translucent
Specific gravity 2.65 constant; variable in impure varieties
Optical properties Uniaxial (+) (Positive)
Refractive index nω = 1.543–1.553 nε = 1.552–1.554
Birefringence +0.009 (B-G interval)
Pleochroism None
Melting point 1650±75 °C
Solubility H2O insoluble
Other characteristics Piezoelectric

Amethyst is a violet variety of quartz often used in jewelry. The name comes from the Ancient Greek a- (“not”) and methustos(“intoxicated”), a reference to the belief that the stone protected its owner from drunkenness; the ancient Greeks and Romans wore amethyst and made drinking vessels of it in the belief that it would prevent intoxication.


Amethyst is the violet variety of quartz; its chemical formula is SiO2.

In the 20th century, the color of amethyst was attributed to the presence of manganese. However, since it is capable of being greatly altered and even discharged by heat, the color was believed by some authorities to be from an organic source. Ferric thiocyanatewas suggested, and sulfur was said to have been detected in the mineral.

More recent work has shown that amethysts’ coloration is due to ferric iron impurities.[1]Further study has shown a complex interplay of iron and aluminium is responsible for the color.[2]

On exposure to heat, amethyst generally becomes yellow, and much of the citrinecairngorm, or yellow quartz of jewelry is said to be merely “burnt amethyst”. Veins of amethystine quartz are apt to lose their color on the exposed outcrop[citation needed].

Synthetic amethyst is made to imitate the best quality amethyst. Its chemical and physical properties are so similar to that of natural amethyst that it can not be differentiated with absolute certainty without advanced gemological testing (which is often cost-prohibitive). There is one test based on “Brazil law twinning” (a form of quartz twinning where right and left hand quartz structures are combined in a single crystal[3]) which can be used to identify synthetic amethyst rather easily. In theory however it is possible to create this material synthetically as well, but this type is not available in large quantities in the market.[4]


Amethyst is composed of an irregular superposition of alternate lamellae of right-handed and left-handed quartz. It has been shown that this structure may be due to mechanical stresses.

Because it has a hardness of seven on the Mohs scale, amethyst is suitable for use in jewelery.

Hue and tone

Amethyst occurs in primary hues from a light pinkish violet to a deep purple. Amethyst may exhibit one or both secondary hues, red and blue. The ideal grade is called “Deep Siberian” and has a primary purple hue of around 75–80 percent, 15–20 percent blue and (depending on the light source) red secondary hues.[4]

The inside of an AmethystGeode.

Cut Amethyst

Cut Green Amethyst


Amethyst was used as a gemstone by the ancient Egyptians and was largely employed in antiquity for intaglios. The Greeks believed amethyst gems could prevent intoxication, while medieval European soldiers wore amethyst amulets as protection in battle.[citation needed]Beads of amethyst were found in Anglo-Saxon graves in England.[citation needed]

A huge geode, or “amethyst-grotto”, from near Santa Cruz in southern Brazil was exhibited at the Düsseldorf, Germany Exhibition of 1902.


The Greek word “amethystos” may be translated as “not drunken”. Amethyst was considered to be a strong antidote against drunkenness, which is why wine goblets were often carved from it. In Greek mythology, Dionysus, the god of intoxication, was pursuing a maiden named Amethystos, who refused his affections.. Amethystos prayed to the gods to remain chaste, which the goddess Artemis granted and transformed her into a white stone. Humbled by Amethystos’s desire to remain chaste, Dionysus poured wine over the stone as an offering, dyeing the crystals purple.

Variations of the story include that Dionysus had been insulted by a mortal and swore to slay the next mortal who crossed his path, creating fierce tigers to carry out his wrath.. The mortal turned out to be a beautiful young woman, Amethystos, who was on her way to pay tribute to Artemis. Her life is spared by Artemis, who transformed the maiden into a statue of pure crystalline quartz to protect her from the brutal claws. Dionysus wept tears of wine in remorse for his action at the sight of the beautiful statue. The god’s tears then stained the quartz purple.[5] Another variation involves the goddess Rhea presenting Dionysus with the amethyst stone to preserve the wine-drinker’s sanity.[6]

Geographic distribution

Amethyst is produced in abundance from the state of Minas Gerais in Brazil where it occurs in large geodes within volcanic rocks. It is also found and mined in South Korea. The largest opencast amethyst vein in the world is in Maissau, Lower Austria. Many of the hollow agates of Brazil and Uruguay contain a crop of amethyst crystals in the interior. Much fine amethyst comes from Russia, especially from near Mursinka in the Ekaterinburg district, where it occurs in drusy cavities in granitic rocks. Many localities in Indiayield amethyst. One of the largest global amethyst producers is Zambia with an annual production of about 1,000 t.

Museum-quality piece of Amethyst

Amethyst occurs at many localities in the United States, but these specimens are rarely fine enough for use in jewelry. Among these may be mentioned Amethyst Mountain, Texas;Yellowstone National ParkDelaware County, PennsylvaniaHaywood County, North Carolina; Deer Hill and Stow, Maine. It is found also in the Lake Superior region. Amethyst is relatively common in Ontario, and in various locations throughout Nova Scotia, but uncommon elsewhere in Canada.


Traditionally included in the cardinal, or most valuable, gemstones (along with diamond,sapphireruby, and emerald), amethyst has lost much of its value due to the discovery of extensive deposits in locations such as Brazil. The highest grade amethyst (called “Deep Russian”) is exceptionally rare and therefore its value is dependent on the demand of collectors when one is found. It is however still orders of magnitude lower than the highest grade sapphires or rubies (Padparadscha sapphire or “pigeon’s blood” ruby).[4]



For other uses, see Quartz (disambiguation).

Quartz crystal group from Tibet
Category Oxide mineral
Chemical formula Silica (silicon dioxide, SiO2)
Color Clear (if no impurities); also see Varieties
Crystal habit 6-sided prism ending in 6-sided pyramid (typical)
Crystal system rhombohedral class 32
Twinning Dauphine law, Brazil law and Japan law
Cleavage None
Fracture Conchoidal
Mohs Scalehardness 7 – lower in impure varieties
Luster Vitreous/glossy
Streak White
Diaphaneity Transparent to translucent
Specific gravity 2.65 constant; variable in impure varieties
Optical properties Uniaxial (+)
Refractive index nω = 1.543 – 1.545 nε = 1.552 – 1.554
Birefringence +0.009 (B-G interval)
Pleochroism None
Melting point 1650 (±75) °C
Solubility 11.0 +/- 1.1 PPM @ 25 C
Other characteristics Piezoelectric

Quartz (from German De-Quarz.ogg Quarz (help·info)[1]) is the second most abundant mineral in the Earth‘s continental crust (after feldspar). It is made up of a continuous framework of SiO4 silicon-oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall formula SiO2.

Crystal habit

Quartz belongs to the rhombohedral crystal system. The ideal crystal shape is a six-sided prismterminating with six-sided pyramidsat each end. In nature quartz crystals are often twinned, distorted, or so intergrown with adjacent crystals of quartz or other minerals as to only show part of this shape, or to lack obvious crystal faces altogether and appear massive. Well-formed crystals typically form in a ‘bed’ that has unconstrained growth into a void, but because the crystals must be attached at the other end to a matrix, only one termination pyramid is present. A quartz geode is such a situation where the void is approximately spherical in shape, lined with a bed of crystals pointing inward.



Pure quartz, sometimes called clear quartz, is colorless or white and transparent (clear) or translucent. Common colored varieties include citrine, rose quartz, amethyst, smoky quartz, milky quartz, and others. Quartz goes by an array of different names. The most important distinction between types of quartz is that of macrocrystalline (individual crystals visible to the unaided eye) and themicrocrystalline orcryptocrystalline varieties (aggregates of crystals visible only under high magnification). The cryptocrystalline varieties are either translucent or mostly opaque, while the transparent varieties tend to be macrocrystalline. Chalcedony is a cryptocrystalline form of silica consisting of fine intergrowths of both quartz, and its monoclinic polymorph moganite.[2]


“Citrine” redirects here. For other uses, see Citrine (disambiguation).


Citrine is a variety of quartz whose color ranges from a pale yellow to brown. It is nearly impossible to tell cut citrine from yellowtopaz visibly. Citrine has ferric impurities, and is rarely found naturally. Most commercial citrine is in fact artificially heated amethystor smoky quartzBrazil is the leading producer of citrine, with much of its production coming from the state of Rio Grande do Sul.

Citrine is one of three traditional birthstones for the month of November.

Rose quartz

Rose Quartz

An elephant carved in rose quartz, 4 inches (10 cm) long

Rose quartz is a type of quartz which exhibits a pale pink to rose red hue. The color is usually considered as due to trace amounts of titaniumiron, or manganese, in the massive material. Some rose quartz contains microscopic rutile needles which produces anasterism in transmitted light. Recent X-ray diffraction studies suggest that the color is due to thin microscopic fibers of possiblydumortierite within the massive quartz.[3]

In crystal form (rarely found) it is called pink quartz and its color is thought to be caused by trace amounts of phosphate oraluminium. The color in crystals is apparently photosensitive and subject to fading. The first crystals were found in a pegmatite found near RumfordMaine, USA, but most crystals on the market come from Minas GeraisBrazil..[4]

Rose quartz is not popular as a gem – it is generally too clouded by impurities to be suitable for that purpose. Rose quartz is more often carved into figures such as people or hearts. Hearts are commonly found because rose quartz is pink and an affordable mineral.


Main article: Amethyst

Amethyst is a popular form of quartz that ranges from a bright to dark or dull purple/violet color.

Smoky quartz

Smokey quartz is a gray, translucent version of quartz. It ranges in clarity from almost complete transparency to a brownish-grey crystal that is almost opaque.

Milky quartz

Milk quartz sample

Milk quartz or milky quartz may be the most common variety of crystalline quartz and can be found almost anywhere. The white colour may be caused by minute fluid inclusions of gas and/or liquid trapped during the crystal formation. The cloudiness caused by the inclusions effectively bars its use in most optical and quality gemstone applications.[5]

Major varieties

Although many of the varietal names historically arose from the color of the mineral, current scientific naming schemes refer primarily to the microstructure of the mineral. Color is a secondary identifier for the cryptocrystalline minerals, although it is a primary identifier for the macrocrystalline varieties. This does not always hold true.

Major Varieties of Quartz
Chalcedony Cryptocrystalline quartz and moganite mixture. The term is generally only used for white or lightly colored material. Otherwise more specific names are used.
Agate Multi-colored, banded chalcedony, semi-translucent to translucent
Onyx Agate where the bands are straight, parallel and consistent in size.
Jasper Opaque cryptocrystalline quartz, typically red to brown
Aventurine Translucent chalcedony with small inclusions (usually mica) that shimmer.
Tiger’s eye Fibrous gold to red-brown coloured quartz, exhibiting chatoyancy.
Rock crystal Clear, colorless
Amethyst Purple, transparent
Citrine Yellow to reddish orange to brown, greenish yellow
Prasiolite Mint green, transparent
Rose quartz Pink, translucent, may display diasterism
Rutilated quartz Contains acicular (needles) inclusions of rutile
Milk quartz White, translucent to opaque, may display diasterism
Smoky quartz Brown to grey, opaque
Carnelian Reddish orange chalcedony, translucent
Rose quartz
Rutilated quartz crystal
Smoky quartz

Quartz sand from Coral Pink Sand Dunes State ParkUtah. These have ahematite coating which provides the orange color. Scale bar is 1.0 mm.

Rutile in quarz

Synthetic and artificial treatments

A synthetic quartz crystal grown by the hydrothermal method, about 19 cm long and weighing about 127 grams.

Not all varieties of quartz are naturally occurring. Prasiolite, an olive colored material, is produced by heat treatment; natural prasiolite has also been observed in Lower Silesia in Poland. Although citrine occurs naturally, the majority is the result of heat-treated amethyst. Carnelian is widely heat-treated to deepen its color.

Due to natural quartz being so often twinned, much of the quartz used in industry is synthesized. Large, flawless and untwinned crystals are produced in an autoclave via the hydrothermal processemeralds are also synthesized in this fashion. While these are still commonly referred to as quartz, the correct term for this material is silicon dioxide.


Quartz is an essential constituent of granite and other felsic igneous rocks. It is very common insedimentary rocks such assandstone and shale and is also present in variable amounts as an accessory mineral in most carbonate rocks. It is also a common constituent of schistgneissquartzite and othermetamorphic rocks. Because of its resistance to weathering it is very common in stream sediments and in residual soils.

Quartz occurs in hydrothermal veins as gangue along with ore minerals. Large crystals of quartz are found in pegmatites. Well-formed crystals may reach several meters in length and weigh hundreds of kilograms.

Related silica minerals

Tridymite and cristobalite are high-temperature polymorphs of SiO2 that occur in high-silica volcanic rocks.Coesite is a denser polymorph of quartz found in some meteorite impact sites and in metamorphic rocks formed at pressures greater than those typical of the Earth’s crust. Stishovite is a yet denser and higher-pressure polymorph of quartz found in some meteorite impact sites.Lechatelierite is an amorphous silicaglass SiO2 which is formed by lightning strikes in quartz sand.


Quartz crystal showingtransparency.

The name “quartz” comes from the German “Quarz”, which is of Slavic origin (Czech miners called itkřemen). Other sources insist the name is from the Saxon word “Querkluftertz”, meaning cross-vein ore.[6]

Quartz is the most common material identified as the mystical substance maban in Australian Aboriginal mythology. It is found regularly in passage tomb cemeteries in Europe in a burial context, eg. Newgrange orCarrowmore in the Republic of Ireland. The Irishword for quartz is grian cloch, which means ‘stone of the sun’.

Roman naturalist Pliny the Elder believed quartz to be water ice, permanently frozen after great lengths of time. (The word “crystal” comes from the Greek word for purity.) He supported this idea by saying that quartz is found near glaciers in the Alps, but not on volcanic mountains, and that large quartz crystals were fashioned into spheres to cool the hands. He also knew of the ability of quartz to split light into a spectrum. This idea persisted until at least the 1600s.

In the 17th century, Nicolas Steno‘s study of quartz paved the way for modern crystallography. He discovered that no matter how distorted a quartz crystal, the long prism faces always made a perfect 60 degree angle.

Charles Sawyer invented the commercial quartz crystal manufacturing process in ClevelandOhioUnited States. This initiated the transition from mined and cut quartz for electrical appliances to manufactured quartz.

Quartz’s piezoelectric properties were discovered by Jacques and Pierre Curie in 1880. The quartz oscillatoror resonator was first developed by Walter Guyton Cady in 1921.[7] George Washington Pierce designed and patented quartz crystal oscillators in 1923.[8]Warren Marrison created the first quartz oscillator clock based on the work of Cady and Pierce in 1927.[9]


Quartz crystals have piezoelectric properties; they develop an electric potential upon the application ofmechanical stress. An early use of this property of quartz crystals was in phonograph pickups. One of the most common piezoelectric uses of quartz today is as a crystal oscillator. The quartz clock is a familiar device using the mineral. The resonant frequency of a quartz crystal oscillator is changed by mechanically loading it, and this principle is used for very accurate measurements of very small mass changes in thequartz crystal microbalance and in thin-film thickness monitors.



“Kunzite” redirects here. For the Sailor Moon character, see Shitennou.

An almost colorless kunzite crystal (upper left), a cut pale pink kunzite (upper right) and a greenish hiddenite crystal (below) (unknown scale)
Category Mineral
Chemical formula lithium aluminium silicate, LiAl(SiO3)2
Color Highly variable: white, colorless, gray, pink, lilac, violet, yellow and green
Crystal habit prismatic, generally flattened and elongated
Crystal system monoclinic; 2/m
Cleavage Perfect prismatic, two directions at nearly 90°
Fracture Sub-conchoidal
Mohs Scalehardness 6.5 – 7
Luster Vitreous
Streak white
Specific gravity 3.17-3.19
Refractive index 1.66-1.68
Pleochroism Strong in kunzite: pink, colorless; hiddenite: yellow-green, blue-green
Fusibility 3.5
Solubility insoluble
Other characteristics Tenebrescencechatoyancy, kunzite often fluorescentunderUV

Spodumene is a pyroxene mineral consisting of lithium aluminium inosilicateLiAl(SiO3)2 – and is a source of lithium. It occurs as colorless to yellowish, purplish or lilac kunzite (see below), yellowish-green or emerald-green hiddenite, prismatic crystals, often of great size. Single crystals of 14.3 m in size are reported from the Black Hills of South DakotaUnited States.[1]

Crystals form in the monoclinic system and are typically heavily striated parallel to the principal axis. Crystal faces are often etched and pitted with triangular markings.

Spodumene is derived from the Greek spodumenos (σποδυμενος), meaning “burnt to ashes,” owing to the opaque, ash-grey appearance of material refined for use in industry.

Spodumene occurs in lithium rich granites and pegmatites. Transparent material has long been used as a gemstone with varieties kunzite and hiddenite noted for their strongpleochroism. Source localities include AfghanistanAustraliaBrazilMadagascar,Pakistanand USA (North CarolinaCalifornia).

Economic importance

Spodumene is an important source of lithium for use in ceramicsmobile phone andautomotive batteriesmedicine and as a fluxing agent. Lithium is extracted from spodumene by fusing in acid.

World production of lithium via spodumene is around 80,000 metric tonnes per annum, primarily from the Greenbushes pegmatite ofWestern Australia, and some Chinese andChilean sources. The Talison mine in Greenbushes, Western Australia has an estimated reserve of 13 million tonnes.[2]

Spodumene is becoming less important a source of lithium due to the emergence of alkalinebrine lake sources in Chile, China andArgentina, which produce lithium chloride directly. Lithium chloride is converted to lithium carbonate and lithium hydroxide by reaction withsodium carbonate and calcium hydroxide respectively.


See the pleochroism and the typical etched marks (unknown scale)

Kunzite is a pink to lilac colored gemstone, a variety of spodumene with the color coming from minor to trace amounts ofmanganese. Some (but not all) kunzite used for gemstones has been heated to enhance its color. It is also frequently irradiated to enhance the color. Many kunzites fade when exposed to sunlight. It was discovered in 1902, and was named after George Frederick KunzTiffany & Co‘s chief jeweler at the time, and a noted mineralogist. It has been found in Brazil, USA, CanadaCISMexico,SwedenWestern AustraliaAfghanistan and Pakistan.




Schorl Tourmaline
Category Silicate mineral group
Chemical formula (Ca,K,Na,[])(Al,Fe,Li,Mg,Mn)3(Al,Cr, Fe,V)6
Color Most commonly black, but can range from brown, violet, green, pink, or in a dual-colored pink and green.
Crystal habit Parallel and elongated. Acicular prisms, sometimes radiating. Massive. Scattered grains (in granite).
Crystal system Trigonal
Cleavage Indistinct
Fracture Uneven, small conchoidal, brittle
Mohs Scalehardness 7–7.5
Luster Vitreous, sometimes resinous
Streak White
Specific gravity 3.06 (+.20 -.06)[1]
Density 2.82–3.32
Polish luster Vitreous[1]
Optical properties Double refractive, uniaxial negative[1]
Refractive index nω=1.635–1.675, nε=1.610–1.650
Birefringence -0.018 to -0.040; typically about .020 but in dark stones it may reach .040[1]
Pleochroism typically moderate to strong[1]
Red Tourmaline: Definite; dark red,light red
Green Tourmaline: Strong; dark green, yellow-green
Brown Tourmaline: Definite; dark brown, light brown
Blue Tourmaline: Strong; dark blue, light blue
Dispersion .017[1]
Ultravioletfluorescence pink stones—inert to very weak red to violet in long and short wave[1]
Absorption spectra a strong narrow band at 498nm, and almost complete absorption of red down to 640nm in blue and green stones; red and pink stones show lines at 458 and 451nm as well as a broad band in the green spectrum[1]

Tourmaline is a crystal silicate mineral compounded with elements such as aluminiumiron,magnesiumsodiumlithium, orpotassium. Tourmaline is classed as a semi-precious stone and the gem comes in a wide variety of colors. The name comes from the Sinhalese word “turamali” or “toramalli”, which applied to different gemstones found in Ceylon (now Sri Lanka).


Brightly colored Sri Lankan gem tourmalines were brought to Europe in great quantities by theDutch East India Company to satisfy a demand for curiosities and gems. At the time it was not realised that schorl and tourmaline were the same mineral.

Tourmaline species and varieties

  • Dravite species: from the Drave district of Carinthia
    • Dark yellow to brownish black—dravite
  • Schorl Species:
    • Bluish or brownish black to Black—schorl
  • Elbaite Species: named after the island of ElbaItaly
    • Rose or pink—rubellite variety(from ruby)
    • Dark black—schorl(from indigo)
    • Light blue to bluish green—Brazilian indicolite variety
    • Green—verdelite or Brazilian emerald variety
    • Colorless—achroite variety (from the Greek for “colorless”)


The most common species of tourmaline is schorl. It may account for 95% or more of all tourmaline in nature. The early history of the mineral schorl shows that the name “schorl” was in use prior to 1400 AD because a village known today as Zschorlau (inSaxonyGermany) was then named “Schorl” (or minor variants of this name). This village had a nearby tin mine where, in addition tocassiterite, black tourmaline was found. The first description of schorl with the name “schürl” and its occurrence (various tin mines in the Saxony Ore Mountains) was written by Johannes Mathesius (1504–1565) in 1562 under the title “Sarepta oder Bergpostill” (Ertl, 2006). Up to about 1600, additional names used in the German languagewere “Schurel”, “Schörle”, and “Schurl”. From the 18th century on, the name “Schörl” was mainly used in the German-speaking area. In English, the names “shorl” and “shirl” were used in the 18th century for schorl. In the 19th century the names “common schorl”, “schörl”, “schorl” and “iron tourmaline” were used in the Anglo-Saxon area (Ertl, 2006). The word tourmaline has two etymologies, both from the Sinhalese word turamali, meaning “stone attracting ash” (a reference to its pyroelectric properties) or according to other sources “mixed gemstones”.


The name dravite was used for the first time by Gustav Tschermak (1836 – 1927; Professor of Mineralogy and Petrography at the University of Vienna) in his book “Lehrbuch der Mineralogie” (published in 1884) for Mg-rich (and Na-rich) tourmaline from the village Unterdrauburg, Drava river area, Carinthia, Austro-Hungarian Empire. Today this tourmaline locality (type locality for dravite) at the village Dravograd (near Dobrova pri Dravogradu), is a part of the Republic of Slovenia (Ertl, 2007). Tschermak gave this tourmaline the name dravite, for the Drava river area, which is the district along the Drava River (in German: Drau, in Latin: Drave) in Austria and Slovenia. The chemical composition which was given by Tschermak in 1884 for this dravite approximately corresponds to the formula NaMg3(Al,Mg)6B3Si6O27(OH), which is in good agreement (except for the OH content) with the endmember formula of dravite as known today (Ertl, 2007).


A lithium-tourmaline (elbaite) was one of three pegmatitic minerals from Utö, Sweden, in which the new alkali element lithium (Li) was determined in 1818 by Arfwedson for the first time (Ertl, 2008). Elba Island, Italy,was one of the first localities where colored and colorless Li-tourmalines were extensively chemically analysed. In 1850 Rammelsberg described fluorine in tourmaline for the first time. In 1870 he proved that all varieties of tourmaline contain chemically bound water. In 1889 Scharitzer proposed the substitution of (OH) by F in red Li-tourmaline from Sušice, Czech Republic. In 1914 Vernadsky proposed the name “Elbait” for Li-,Na-, and Al-rich tourmaline from Elba Island, Italy, with the simplified formula (Li,Na)HAl6B2Si4O21 (Ertl, 2008). Most likely the type material for elbaite was found at Fonte del Prete, San Piero in Campo, Campo nell’Elba, Elba Island, Livorno Province, Tuscany, Italy (Ertl, 2008). In 1933 Winchell published an updated formula for elbaite, H8Na2Li3Al3B6Al12Si12O62, which is commonly used to date written as Na(Li1.5Al1.5)Al6(BO3)3[Si6O18](OH)3(OH) (Ertl, 2008). The first crystal structure determination of a Li-rich tourmaline was published in 1972 by Donnay and Barton, performed on a pink elbaite from San Diego County, California, U.S.A.

Chemical composition tourmaline group

The tourmaline mineral group is chemically one of the most complicated groups of silicate minerals. Its composition varies widely because of isomorphous replacement (solid solution), and its general formula can be written as



X = CaNaK, vacancy

Y = LiMgFe2+Mn2+ZnAlCr3+V3+Fe3+Ti4+, vacancy

Z = Mg, Al, Fe3+, Cr3+, V3+

T = Si, Al, B

B = B, vacancy

V = OH, O

W = OH, F, O

The 14 recognized minerals in the group (endmember formulas)
Buergerite NaFe3+3Al6Si6O18(BO3)3O3F
Chromdravite NaMg3Cr6Si6O18(BO3)3(OH)4
Dravite NaMg3Al6Si6O18(BO3)3(OH)4
Elbaite Na(Li1.5,Al1.5)Al6Si6O18(BO3)3(OH)4
Feruvite CaFe2+3(MgAl5)Si6O18(BO3)3(OH)4
Foitite (Fe2+2Al)Al6Si6O18(BO3)3(OH)4
Liddicoatite Ca(Li2Al)Al6Si6O18(BO3)3(OH)3F
Magnesiofoitite (Mg2Al)Al6Si6O18(BO3)3(OH)4
Olenite NaAl3Al6Si6O18(BO3)3O3OH
Povondraite NaFe3+3(Fe3+4Mg2)Si6O18(BO3)3(OH)3O
Rossmanite (LiAl2)Al6Si6O18(BO3)3(OH)4
Schorl NaFe2+3Al6Si6O18(BO3)3(OH)4
Uvite CaMg3(MgAl5)Si6O18(BO3)3(OH)3F
Vanadiumdravite NaMg3V6Si6O18(BO3)3(OH)4

Tri-color elbaite crystals on quartz, Himalaya Mine, San Diego Co., California, USA

Physical properties

Crystal structure

Tourmaline belongs to the trigonal crystal system and occurs as long, slender to thick prismatic and columnar crystals that are usually triangular in cross-section. The style of termination at the ends of crystals is asymmetrical, called hemimorphism. Small slender prismatic crystals are common in a fine-grained granite called aplite, often forming radial daisy-like patterns. Tourmaline is distinguished by its three-sided prisms; no other common mineral has three sides. Prisms faces often have heavy vertical striations that produce a rounded triangular effect. Tourmaline is rarely perfectly euhedral. An exception was the fine dravite tourmalines ofYinnietharra, in western Australia. The deposit was discovered in the 1970s, but is now exhausted. All hemimorphic crystals arepiezoelectric, and are oftenpyroelectric as well.


Tourmaline has a variety of colors. Usually, iron-rich tourmalines are black to bluish-black to deep brown, while magnesium-rich varieties are brown to yellow, and lithium-rich tourmalines are almost any color: blue, green, red, yellow, pink etc. Rarely, it is colorless. Bi-colored and multicolored crystals are common, reflecting variations of fluid chemistry during crystallisation. Crystals may be green at one end and pink at the other, or green on the outside and pink inside: this type is called watermelon tourmaline. Some forms of tourmaline are dichroic, in that they change color when viewed from different directions.

Large pink elbaite crystal on quartz, Cryo-Genie Mine, San Diego Co., California, USA.


Some tourmaline gems, especially pink to red colored stones, are altered by irradiation to improve their color. Irradiation is almost impossible to detect in tourmalines, and does not impact the value. Heavily-included tourmalines, such as rubellite and Brazilian paraiba, are sometimes clarity enhanced. A clarity-enhanced tourmaline (especially paraiba) is worth much less than a non-treated gem.[4]


Tourmaline is found in two main geological occurrences. Igneous rocks, in particular graniteand granite pegmatite and inmetamorphic rocks such as schist and marble. Schorl and lithium-rich tourmalines are usually found in granite and granitepegmatite. Magnesium-rich tourmalines, dravites, are generally restricted to schists and marble. Tourmaline is a durable mineral and can be found in minor amounts as grains in sandstone and conglomerate.

Bi-colored tourmaline crystal, 0.8 inches long (2 cm).

Tourmaline localities

Gem and specimen tourmaline is mined chiefly in Brazil and Africa. Some placer material suitable for gem use comes from Sri Lanka. In addition to Brazil, tourmaline is mined inTanzaniaNigeriaKenyaMadagascarMozambiqueNamibiaAfghanistan,Pakistan, andSri Lanka, and Malawi.[5]

United States

Some fine gems and specimen material has been produced in the United States, with the first discoveries in 1822, in the state ofMaineCalifornia became a large producer of tourmaline in the early 1900s. The Maine deposits tend to produce crystals in raspberry pink-red as well as minty greens. The California deposits are known for bright pinks, as well as bicolors. During the early 1900s, Maine and California were the world’s largest producers of gem tourmalines. The Empress Dowager Tz’u Hsi, the last Empress ofChina, loved pink tourmaline and bought large quantities for gemstones and carvings from the then new Himalaya Mine, located inSan Diego County, California. [6] It is not clear when the first tourmaline was found in California.Native Americans have used pink and green tourmaline as funeral gifts for centuries. The first documented case was in 1890 when Charles Russel Orcutt found pink tourmaline at what later became the Stewart Mine at PalaSan Diego [7].


Watermelon Tourmaline mineral on quartz matrix (crystal approximately 2 cm wide at face)

Almost every color of tourmaline can be found in Brazil, especially in the Brazilian states ofMinas Gerais and Bahia. In 1989, miners discovered a unique and brightly colored variety of tourmaline in the state of