domingo, 21 de julho de 2013

Beryl

Beryl


Beryl
Beryl09.jpg
Three varieties of beryl: morganite, aquamarine and heliodor
General
Category Cyclosilicate
Formula
(repeating unit)		 Be3Al2(SiO3)6
Strunz classification 09.CJ.05
Crystal symmetry Hexagonal dihexagonal dipyramidal
H-M symbol (6/m 2/m 2/m)
Space group: P 6/mmc
Unit cell a = 9.21 Å, c = 9.19 Å; Z = 2
Identification
Formula mass 537.50
Color Green, blue, yellow, colorless, pink and others
Crystal habit Prismatic to tabular cystals; radial, columnar; granular to compact massive
Crystal system Hexagonal
Twinning Rare
Cleavage Imperfect on {0001}
Fracture Conchoidal to irregular
Tenacity Brittle
Mohs scale hardness 7.5–8
Luster Vitreous to resinous
Streak White
Diaphaneity Transparent to translucent
Specific gravity Average 2.76
Optical properties Uniaxial (-)
Refractive index nω = 1.564–1.595
nε = 1.568–1.602
Birefringence δ = 0.0040–0.0070
Pleochroism Weak to distinct
Ultraviolet fluorescence None (some fracture filling materials used to improve emerald's clarity do fluoresce, but the stone itself does not)
References [1][2][3]
In geology, beryl is a mineral composed of beryllium aluminium cyclosilicate with the chemical formula Be3Al2(SiO3)6. The hexagonal crystals of beryl may be very small or range to several meters in size. Terminated crystals are relatively rare. Pure beryl is colorless, but it is frequently tinted by impurities; possible colors are green, blue, yellow, red, and white.

Contents

Etymology

The name beryl is derived (via Latin: beryllus, Old French: beryl, and Middle English: beril) from Greek βήρυλλος beryllos which referred to a "precious blue-green color-of-sea-water stone"[1] and originated from Prakrit veruliya (वॆरुलिय‌) and Pali veḷuriya (वेलुरिय); veḷiru (भेलिरु); from Sanskrit वैडूर्य vaidurya-, which is ultimately of Dravidian origin, maybe from the name of Belur or "Velur" in southern India.[4] The term was later adopted for the mineral beryl more exclusively.[2] The Late Latin word berillus was abbreviated as brill- which produced the Italian word brillare meaning "shine", the French word brille meaning "shine", the Spanish word brillo, also meaning "shine", and the English word brilliance.[5]
Morganite and aquamarine together to show contrast

Deposits

Beryl of various colors is found most commonly in granitic pegmatites, but also occurs in mica schists in the Ural Mountains, and limestone in Colombia. Beryl is often associated with tin and tungsten ore bodies. Beryl is found in Europe in Norway, Austria, Germany, Sweden (especially morganite), Ireland and Russia, as well as Brazil, Colombia, Madagascar, Mozambique, South Africa, the United States, and Zambia. US beryl locations are in California, Colorado, Connecticut, Idaho, Maine, New Hampshire, North Carolina, South Dakota and Utah.
New England's pegmatites have produced some of the largest beryls found, including one massive crystal from the Bumpus Quarry in Albany, Maine with dimensions 5.5 by 1.2 m (18 by 3.9 ft) with a mass of around 18 metric tons; it is New Hampshire's state mineral. As of 1999, the world's largest known naturally occurring crystal of any mineral is a crystal of beryl from Malakialina, Madagascar, 18 meters long and 3.5 meters in diameter, and weighing 380,000 kilograms.[6]

Varieties

Aquamarine and maxixe

Aquamarine
Aquamarine (from Latin: aqua marina, "water of the sea") is a blue or turquoise variety of beryl. It occurs at most localities which yield ordinary beryl. The gem-gravel placer deposits of Sri Lanka contain aquamarine. Clear yellow beryl, such as that occurring in Brazil, is sometimes called aquamarine chrysolite.[citation needed] The deep blue version of aquamarine is called maxixe. Maxixe is commonly found in the country of Madagascar. Its color fades to white when exposed to sunlight or is subjected to heat treatment, though the color returns with irradiation.
The pale blue color of aquamarine is attributed to Fe2+. The Fe3+ ions produce golden-yellow color, and when both Fe2+ and Fe3+ are present, the color is a darker blue as in maxixe. Decoloration of maxixe by light or heat thus may be due to the charge transfer Fe3+ and Fe2+.[7][8][9][10] Dark-blue maxixe color can be produced in green, pink or yellow beryl by irradiating it with high-energy particles (gamma rays, neutrons or even X-rays).[11]
In the United States, aquamarines can be found at the summit of Mt. Antero in the Sawatch Range in central Colorado. In Wyoming, aquamarine has been discovered in the Big Horn Mountains, near Powder River Pass. In Brazil, there are mines in the states of Minas Gerais, Espírito Santo, and Bahia, and minorly in Rio Grande do Norte. The mines of Colombia, Zambia, Madagascar, Malawi, Tanzania and Kenya also produce aquamarine.
The largest aquamarine of gemstone quality ever mined was found in Marambaia, Minas Gerais, Brazil, in 1910. It weighed over 110 kg, and its dimensions were 48.5 cm (19 in) long and 42 cm (17 in) in diameter.[12] The largest cut aquamarine gem is the Dom Pedro aquamarine, now housed in the Smithsonian Institution's National Museum of Natural History.[13]

Emerald

Main article: Emerald
Rough emerald on matrix
Emerald refers to green beryl, colored by trace amounts of chromium and sometimes vanadium.[7][14] The word "emerald" comes (via Middle English: Emeraude, imported from Old French: Ésmeraude and Medieval Latin: Esmaraldus) from Latin smaragdus from Greek smaragdos – σμάραγδος ("green gem"), its original source being a Semitic word izmargad (אזמרגד) or the Sanskrit word, marakata (मरकन), meaning "green".[15] Most emeralds are highly included, so their brittleness (resistance to breakage) is classified as generally poor.
Emeralds in antiquity were mined by the Egyptians and in Austria, as well as Swat in northern Pakistan.[16] A rare type of emerald known as a trapiche emerald is occasionally found in the mines of Colombia. A trapiche emerald exhibits a "star" pattern; it has raylike spokes of dark carbon impurities that give the emerald a six-pointed radial pattern. It is named for the trapiche, a grinding wheel used to process sugarcane in the region. Colombian emeralds are generally the most prized due to their transparency and fire. Some of the most rare emeralds come from three main emerald mining areas in Colombia: Muzo, Coscuez, and Chivor. Fine emeralds are also found in other countries, such as Zambia, Brazil, Zimbabwe, Madagascar, Pakistan, India, Afghanistan and Russia. In the US, emeralds can be found in Hiddenite, North Carolina. In 1998, emeralds were discovered in the Yukon.
Emerald is a rare and valuable gemstone and, as such, it has provided the incentive for developing synthetic emeralds. Both hydrothermal[17] and flux-growth synthetics have been produced. The first commercially successful emerald synthesis process was that of Carroll Chatham.[18] The other large producer of flux emeralds was Pierre Gilson Sr., which has been on the market since 1964. Gilson's emeralds are usually grown on natural colorless beryl seeds which become coated on both sides. Growth occurs at the rate of 1 mm per month, a typical seven-month growth run producing emerald crystals of 7 mm of thickness.[19] The green color of emeralds is attributed to presence of Cr3+ ions.[8][9][10]
Golden beryl
Heliodor

Golden beryl and heliodor

Golden beryl can range in colors from pale yellow to a brilliant gold. Unlike emerald, golden beryl has very few flaws. The term "golden beryl" is sometimes synonymous with heliodor (from Greek hēlios – ἥλιος "sun" + dōron – δῶρον "gift") but golden beryl refers to pure yellow or golden yellow shades, while heliodor refers to the greenish-yellow shades. The golden yellow color is attributed to Fe3+ ions.[7][8] Both golden beryl and heliodor are used as gems. Probably the largest cut golden beryl is the flawless 2054 carat stone on display in the Hall of Gems, Washington, D.C.[20]
Golden beryl, oval cut

Goshenite

Goshenite
Colorless beryl is called goshenite. The name originates from Goshen, Massachusetts where it was originally discovered. Since all these color varieties are caused by impurities and pure beryl is colorless, it might be tempting to assume that goshenite is the purest variety of beryl. However, there are several elements that can act as inhibitors to color in beryl and so this assumption may not always be true. The name goshenite has been said to be on its way to extinction and yet it is still commonly used in the gemstone markets. Goshenite is found to some extent in almost all beryl localities. In the past, goshenite was used for manufacturing eyeglasses and lenses owing to its transparency. Nowadays, it is most commonly used for gemstone purposes and also considered as a source of beryllium.[21][22]
The gem value of goshenite is relatively low. However, goshenite can be colored yellow, green, pink, blue and in intermediate colors by irradiating it with high-energy particles. The resulting color depends on the content of Ca, Sc, Ti, V, Fe, and Co impurities.[8]

Morganite

Morganite
Morganite, also known as "pink beryl", "rose beryl", "pink emerald", and "cesian (or caesian) beryl", is a rare light pink to rose-colored gem-quality variety of beryl. Orange/yellow varieties of morganite can also be found, and color banding is common. It can be routinely heat treated to remove patches of yellow and is occasionally treated by irradiation to improve its color. The pink color of morganite is attributed to Mn2+ ions.[7]
Pink beryl of fine color and good sizes was first discovered on an island on the coast of Madagascar in 1910.[23] It was also known, with other gemstone minerals, such as tourmaline and kunzite, at Pala, California. In December 1910, the New York Academy of Sciences named the pink variety of beryl "morganite" after financier J. P. Morgan.[23]
On October 7, 1989, one of the largest gem morganite specimens ever uncovered, eventually called "The Rose of Maine," was found at the Bennett Quarry in Buckfield, Maine, US.[24] The crystal, originally somewhat orange in hue, was 23 cm (9 in) long and about 30 cm (12 in) across, and weighed (along with its matrix) just over 50 pounds (23 kg).[25]

Red beryl

Red beryl
Red beryl (also known as "red emerald" or "scarlet emerald") is a red variety of beryl. It was first described in 1904 for an occurrence, its type locality, at Maynard's Claim (Pismire Knolls), Thomas Range, Juab County, Utah.[26][27] The old synonym "bixbite" is deprecated from the CIBJO, because of the risk of confusion with the mineral bixbyite (also named after the mineralogist Maynard Bixby). The dark red color is attributed to Mn3+ ions.[7]
Red beryl is very rare and has only been reported from a handful of locations including: Wah Wah Mountains, Beaver County, Utah; Paramount Canyon and Round Mountain, Sierra County, New Mexico;[1] and Juab County, Utah. The greatest concentration of gem-grade red beryl comes from the Violet Claim in the Wah Wah Mountains of mid-western Utah, discovered in 1958 by Lamar Hodges, of Fillmore, Utah, while he was prospecting for uranium.[28] Prices for top quality natural red beryl can be as high as $10,000 per carat for faceted stones. Red beryl has been known to be confused with pezzottaite, also known as raspberry beryl or "raspberyl", a gemstone that has been found in Madagascar and now Afghanistan – although cut gems of the two varieties can be distinguished from their difference in refractive index.[29]
While gem beryls are ordinarily found in pegmatites and certain metamorphic stones, red beryl occurs in topaz-bearing rhyolites. It is formed by crystallizing under low pressure and high temperature from a pneumatolitic phase along fractures or within near-surface miarolitic cavities of the rhyolite. Associated minerals include bixbyite, quartz, orthoclase, topaz, spessartine, pseudobrookite and hematite.[30]
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Apatite

Apatite


Apatite group
Apatite crystals.jpg
General
Category Phosphate mineral
Formula
(repeating unit)		 Ca5(PO4)3(F,Cl,OH)
Strunz classification 08.BN.05
Identification
Color Transparent to translucent, usually green, less often colorless, yellow, blue to violet, pink, brown.[1]
Crystal habit Tabular, prismatic crystals, massive, compact or granular
Crystal system Hexagonal dipyramidal (6/m)[2]
Cleavage [0001] indistinct, [1010] indistinct[2]
Fracture Conchoidal to uneven[1]
Mohs scale hardness 5[1] (defining mineral)
Luster Vitreous[1] to subresinous
Streak White
Diaphaneity Transparent to translucent[2]
Specific gravity 3.16–3.22[2]
Polish luster Vitreous[1]
Optical properties Double refractive, uniaxial negative[1]
Refractive index 1.634–1.638 (+0.012, −0.006)[1]
Birefringence 0.002–0.008[1]
Pleochroism Blue stones – strong, blue and yellow to colorless. Other colors are weak to very weak.[1]
Dispersion 0.013[1]
Ultraviolet fluorescence Yellow stones – purplish pink which is stronger in long wave; blue stones – blue to light blue in both long and short wave; green stones – greenish yellow which is stronger in long wave; violet stones – greenish yellow in long wave, light purple in short wave.[1]
Apatite is a group of phosphate minerals, usually referring to hydroxylapatite, fluorapatite and chlorapatite, named for high concentrations of OH−, F−, Cl− or ions, respectively, in the crystal. The formula of the admixture of the four most common endmembers is written as Ca10(PO4)6(OH,F,Cl)2, and the crystal unit cell formulae of the individual minerals are written as Ca10(PO4)6(OH)2, Ca10(PO4)6(F)2 and Ca10(PO4)6(Cl)2.
Apatite is one of a few minerals produced and used by biological micro-environmental systems. Apatite is the defining mineral for 5 on the Mohs scale. Hydroxyapatite, also known as hydroxylapatite, is the major component of tooth enamel and bone mineral. A relatively rare form of apatite in which most of the OH groups are absent and containing many carbonate and acid phosphate substitutions is a large component of bone material.
Fluorapatite (or fluoroapatite) is more resistant to acid attack than is hydroxyapatite; in the mid-20th century, it was discovered that communities whose water supply naturally contained fluorine had lower rates of dental caries.[3] Fluoridated water allows exchange in the teeth of fluoride ions for hydroxyl groups in apatite. Similarly, toothpaste typically contains a source of fluoride anions (e.g. sodium fluoride, sodium monofluorophosphate). Too much fluoride results in dental fluorosis and/or skeletal fluorosis.
Fission tracks in apatite are commonly used to determine the thermal history of orogenic (mountain) belts and of sediments in sedimentary basins. (U-Th)/He dating of apatite is also well established for use in determining thermal histories and other, less typical applications such as paleo-wildfire dating.
Phosphorite is a phosphate-rich sedimentary rock, that contains between 18% and 40% P2O5. The apatite in phosphorite is present as cryptocrystalline masses referred to as collophane.

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Uses

Apatity, Russia, a site of apatite mines and processing facilities
The primary use of apatite is in the manufacture of fertilizer – it is a source of phosphorus. It is occasionally used as a gemstone. Green and blue varieties in finely divided form, are pigments with excellent covering power.
During digestion of apatite with sulfuric acid to make phosphoric acid, hydrogen fluoride is produced as a byproduct from any fluorapatite content. This byproduct is a minor industrial source of hydrofluoric acid.[4]
Fluoro-chloro apatite forms the basis of the now obsolete Halophosphor fluorescent tube phosphor system. Dopant elements of manganese and antimony, at less than one mole-percent, in place of the calcium and phosphorus impart the fluorescence, and adjustment of the fluorine to chlorine ratio adjusts the shade of white produced. Now almost entirely replaced by the Tri-Phosphor system.[5]
In the United States, apatite derived fertilizers are used to supplement the nutrition of many agricultural crops by providing a valuable source of phosphate.
Apatites are also a proposed host material for storage of nuclear waste, along with other phosphates.

Gemology

Apatite is infrequently used as a gemstone. Transparent stones of clean color have been faceted, and chatoyant specimens have been cabochon cut.[1] Chatoyant stones are known as cat's-eye apatite,[1] transparent green stones are known as asparagus stone,[1] and blue stones have been called moroxite.[6] If crystals of rutile have grown in the crystal of apatite, in the right light the cut stone displays a cat's eye effect. Major sources for gem apatite are[1] Brazil, Burma, and Mexico. Other sources include[1] Canada, Czech Republic, Germany, India, Madagascar, Mozambique, Norway, South Africa, Spain, Sri Lanka, and the United States.

Use as an ore mineral

Apatite is occasionally found to contain significant amounts of rare earth elements and can be used as an ore for those metals.[7] This is preferable to traditional rare earth ores, as apatite is non-radioactive [8] and does not pose an environmental hazard in mine tailings. However, some apatite in Florida used to produce phosphate for agriculture does contain uranium, radium, lead 210 and polonium 210 and radon.[9][10]
Apatite is an ore mineral at the Hoidas Lake rare earth project.[11]

Thermodynamics

The standard (p = 0.1 MPa) molar enthalpies of formation in the crystalline state of hydroxyapatite, chlorapatite and a preliminary value for bromapatite, at T = 298.15 K, have already been determined by reaction-solution calorimetry. Speculations on the existence of a possible fifth member of the calcium apatites family, iodoapatite, have been drawn from energetic considerations.[12]
Structural and thermodynamic properties of crystal hexagonal calcium apatites, Ca10(PO4)6(X)2 (X= OH, F, Cl, Br), have been investigated using an all-atom Born-Huggins-Mayer potential by a molecular dynamics technique. The accuracy of the model at room temperature and atmospheric pressure was checked against crystal structural data, with maximum deviations of ca. 4% for the haloapatites and 8% for hydroxyapatite. High-pressure simulation runs, in the range 0.5-75 kbar, were performed in order to estimate the isothermal compressibility coefficient of those compounds. The deformation of the compressed solids is always elastically anisotropic, with BrAp exhibiting a markedly different behavior from those displayed by HOAp and ClAp. High-pressure p-V data were fitted to the Parsafar-Mason equation of state with an accuracy better than 1%.[13]
The monoclinic solid phases Ca10(PO4)6(X)2 (X= OH, Cl) and the molten hydroxyapatite compound have also been studied by molecular dynamics.[14][15]

Lunar science

Moon rocks collected by astronauts during the Apollo program contain traces of apatite.[16] Re-analysis of these samples in 2010 revealed water trapped in the mineral as hydroxyl, leading to estimates of water on the lunar surface at a rate of at least 64 parts per billion – 100 times greater than previous estimates – and as high as 5 parts per million.[17] If the minimum amount of mineral-locked water was hypothetically converted to liquid, it would cover the Moon's surface in roughly one meter of water.[18]

See also

Apatite Crystal, Mexico

References

Wikimedia Commons has media related to: Apatite
  1. ^ a b c d e f g h i j k l m n o p Gemological Institute of America, GIA Gem Reference Guide 1995, ISBN 0-87311-019-6
  2. ^ a b c d Apatite. Webmineral
  3. ^ National Institute of Dental and Craniofacial Research. The story of fluoridation; 2008-12-20.
  4. ^ Villalba, Gara; Ayres, Robert U.; Schroder, Hans (2008). "Accounting for Fluorine: Production, Use, and Loss". Journal of Industrial Ecology 11: 85–101. doi:10.1162/jiec.2007.1075.
  5. ^ Henderson and Marsden, "Lamps and Lighting", Edward Arnold Ltd, 1972, ISBN 0-7131-3267-1
  6. ^ Streeter, Edwin W., Precious Stones and Gems 6th edition, George Bell and Sons, London, 1898, p306
  7. ^ Salvi S, Williams‐Jones A. 2004. Alkaline granite‐syenite deposits. In Linnen RL, Samson IM, editors. Rare element geochemistry and mineral deposits. St. Catharines (ON): Geological Association of Canada. pp. 315‐341 ISBN 1-897095-08-2
  8. ^ Haxel G, Hedrick J, Orris J. 2006. Rare earth elements critical resources for high technology. Reston (VA): United States Geological Survey. USGS Fact Sheet: 087‐02.
  9. ^ Proctor, Robert N. (2006-12-01) Puffing on Polonium – New York Times. Nytimes.com. Retrieved on 2011-07-24.
  10. ^ Tobacco Smoke | Radiation Protection | US EPA. Epa.gov (2006-06-28). Retrieved on 2011-07-24.
  11. ^ Great Western Minerals Group Ltd. | Projects – Hoidas Lake, Saskatchewan. Gwmg.ca (2010-01-27). Retrieved on 2011-07-24.
  12. ^ Cruz, F.J.A.L.; Minas da Piedade, M.E.; Calado, J.C.G. (2005). "Standard molar enthalpies of formation of hydroxy-, chlor-, and bromapatite". J. Chem. Thermodyn. 37 (10): 1061–1070. doi:10.1016/j.jct.2005.01.010.
  13. ^ Cruz, F.J.A.L.; Canongia Lopes, J.N.; Calado, J.C.G.; Minas da Piedade, M.E. (2005). "A Molecular Dynamics Study of the Thermodynamic Properties of Calcium Apatites. 1. Hexagonal Phases". J. Phys. Chem. B 109 (51): 24473–24479. doi:10.1021/jp054304p.
  14. ^ Cruz, F.J.A.L.; Canongia Lopes, J.N.; Calado, J.C.G. (2006). "Molecular Dynamics Study of the Thermodynamic Properties of Calcium Apatites. 2. Monoclinic Phases". J. Phys. Chem. B 110 (9): 4387–4392. doi:10.1021/jp055808q.
  15. ^ Cruz, F.J.A.L.; Canongia Lopes, J.N.; Calado, J.C.G. (2006). "Molecular dynamics simulations of molten calcium hydroxyapatite". Fluid Phase Eq. 241 (1-2): 51–58. doi:10.1016/j.fluid.2005.12.021.
  16. ^ Smith, J. V., Anderson, A. T., Newton, R. C., Olsen, E. J., Crewe, A. V., Isaacson, M. S. (1970). "Petrologic history of the moon inferred from petrography, mineralogy and petrogenesis of Apollo 11 rocks". Geochimica et Cosmochimica Acta. 34, Supplement 1: 897–925. Bibcode:1970GeCAS...1..897S. doi:10.1016/0016-7037(70)90170-5.
  17. ^ McCubbina, Francis M.; Steele, Andrew; Haurib, Erik H.; Nekvasilc, Hanna; Yamashitad, Shigeru; Russell J. Hemleya (2010). "Nominally hydrous magmatism on the Moon". Proceedings of the National Academy of Sciences 107 (25): 11223–11228. Bibcode:2010PNAS..10711223M. doi:10.1073/pnas.1006677107.
  18. ^ Fazekas, Andrew "Moon Has a Hundred Times More Water Than Thought" National Geographic News (June 14, 2010). News.nationalgeographic.com (2010-06-14). Retrieved on 2011-07-24.
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Chrysocolla

Chrysocolla


Chrysocolla
Chrysocolla.jpg
Chrysocolla and malachite from Australia
General
Category Silicate mineral
Formula
(repeating unit)		 (Cu,Al)2H2Si2O5(OH)4·nH2O
Strunz classification 09.ED.20
Unit cell a = 5.7 Å, b = 8.9 Å, c = 6.7 Å
Identification
Color Blue, Cyan or blue-green, green
Crystal habit Massive, nodular, botryoidal
Crystal system Orthorhombic
Cleavage none
Fracture Irregular/uneven, sub-conchoidal
Tenacity Brittle to sectile
Mohs scale hardness 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 Biaxial (-)
Refractive index nα = 1.575 - 1.585 nβ = 1.597 nγ = 1.598 - 1.635
Birefringence δ = 0.023 - 0.050
References [1][2][3]
Chrysocolla is a hydrated copper silicate mineral with formula (Cu,Al)2H2Si2O5(OH)4·nH2O.

Contents

Properties

Powder-blue chrysocolla as stalactitic growths and as a thin carpet in vugs inside a boulder of nearly solid tyrolite from the San Simon Mine, Iquique Province, Chile (size: 14.1 x 8.0 x 7.8 cm)
Chrysocolla has a cyan (blue-green) color and is a minor ore of copper, having a hardness of 2.5 to 3.5.

Name and discovery

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.

Formation and occurrence

Banded white to blue green chrysocolla from Bisbee, Arizona (size: 12.2 x 5.5 x 5.2 cm)
It is of secondary origin and forms in the oxidation zones of copper ore bodies. Associated minerals are quartz, limonite, azurite, malachite, cuprite, and other secondary copper minerals.
It is typically found as botryoidal or rounded masses and crusts, or vein fillings. Because of its light color, it is sometimes confused with turquoise.
Notable occurrences include Israel, Democratic Republic of Congo, Chile, Cornwall in England, and Arizona, Utah, Idaho, New Mexico, Michigan, and Pennsylvania in the United States.

Questions regarding mineral status

A 2006 study has produced evidence that chrysocolla may be a microscopic mixture of the copper hydroxide mineral spertiniite, amorphous silica and water.[4][2]

References

Wikimedia Commons has media related to: Chrysocolla
  1. ^ Handbook of Mineralogy
  2. ^ a b Mindat
  3. ^ Webmineral data
  4. ^ François Farges, Karim Benzerara, Gordon E. Brown, Jr.; Chrysocolla Redefined as Spertiniite; SLAC-PUB-12232; 13th International Conference On X-Ray Absorption Fine Structure (XAFS13); July 9-14, 2006; Stanford, California
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Malachite

Malachite


Malachite
Malachite, Zaire.jpg
Malachite from the Congo
General
Category Carbonate mineral
Formula
(repeating unit)		 Cu2CO3(OH)2
Strunz classification 05.BA.10
Identification
Formula mass 221.1 g/mol
Color Bright green, dark green, blackish green, commonly banded in masses; green to yellowish green in transmitted light
Crystal habit Massive, botryoidal, stalactitic, crystals are acicular to tabular prismatic
Crystal system Monoclinic—prismatic H-M Symbol (2/m) Space group P21/a
Twinning Common as contact or penetration twins on {100} and {201}. Polysynthetic twinning also present.
Cleavage Perfect on {201} fair on {010}
Fracture Subconchoidal to uneven
Mohs scale hardness 3.5–4.0
Luster Adamantine to vitreous; silky if fibrous; dull to earthy if massive
Streak light green
Diaphaneity Translucent to opaque
Specific gravity 3.6–4
Optical properties Biaxial (–)
Refractive index nα = 1.655 nβ = 1.875 nγ = 1.909
Birefringence δ = 0.254
References [1][2][3]
Malachite is a copper carbonate hydroxide mineral, with the formula Cu2CO3(OH)2. This opaque, green banded mineral crystallizes in the monoclinic crystal system, and most often forms botryoidal, fibrous, or stalagmitic masses, in fractures and spaces, deep underground, where the water table and hydrothermal fluids provide the means for chemical precipitation. Individual crystals are rare but do occur as slender to acicular prisms. Pseudomorphs after more tabular or blocky azurite crystals also occur.[3] Typical malachite is laminated and whether or not microbes intervene in its formation is unknown.

Contents

Etymology and history

The stone's name derives (via Latin: molochītis, Middle French: melochite, and Middle English melochites) from Greek Μολοχίτης λίθος molochitis lithos, "mallow-green stone", from μολόχη molōchē, variant of μαλάχη malāchē, "mallow".[4] The mineral was given this name due to its resemblance to the leaves of the Mallow plant.[5]
Malachite was used as a mineral pigment in green paints from antiquity until about 1800. The pigment is moderately lightfast, very sensitive to acids and varying in color. The natural form was being replaced by its synthetic form, verditer among other synthetic greens. It is also used for decorative purposes, such as in the Malachite Room in the Hermitage, which features a huge malachite vase and the Malachite Room in Castillo de Chapultepec in Mexico City. "The Tazza", a large malachite vase, one of the largest pieces of malachite in North America and a gift from Tsar Nicholas II, stands as the focal point in the center of the room of Linda Hall Library.
Archeological evidence indicates that the mineral has been mined and smelted at Timna Valley in Israel for over 3,000 years.[6] Since then, malachite has been used as both an ornamental stone and as a gemstone.

Occurrence

Malachite often results from weathering of copper ores and is often found together with azurite (Cu3(CO3)2(OH)2), goethite, and calcite. Except for its vibrant green color, the properties of malachite are similar to those of azurite and aggregates of the two minerals occur frequently. Malachite is more common than azurite and is typically associated with copper deposits around limestones, the source of the carbonate.
Large quantities of malachite have been mined in the Urals, Russia. It is found worldwide including in the Democratic Republic of Congo; Gabon; Zambia; Tsumeb, Namibia; Mexico; Broken Hill, New South Wales; Lyon, France; Timna Valley, Israel; and the Southwestern United States, most notably in Arizona.[7]

Malachite gallery

See also

References

  1. ^ Malachite in Handbook of Mineralogy
  2. ^ Malachite at Webmineral
  3. ^ a b Malachite at Mindat
  4. ^ Malachite, Dictionary.com
  5. ^ Harper, Douglas. "malachite". Online Etymology Dictionary.
  6. ^ Parr, Peter J review of "Timma: Valley of the Biblical Copper Mines" by Beno Rothenberg Bulletin of the School of Oriental and African Studies, University of London, Vol. 37, No. 1, In Memory of W. H. Whiteley (1974), pp. 223–224
  7. ^ Mindat map with over 8500 locations
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