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Turquoise

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Turquoise is a member of phosphate mineral with chemical the formula CuAl6 (PO4)4(OH) 8·4H2O. Turquoise is an opaque, blue-to-green mineral that is a hydrated phosphate of copper and aluminium. Beads made of turquoise that date back to c.5000 BCE have been recovered in Mesopotamia (present-day Iraq). This mineral usually occurs in massive or microcrystalline forms, as encrustations or nodules, or in veins. Crystals are rare; when found, they occur as short, often transparent prisms. Turquoise varies in color from sky-blue to green, depending on the amount of iron and copper it contains. Turquoise occurs in arid environments as a secondary mineral probably derived from the decomposition of apatite and some copper sulfides. One of the first gemstones to be mined. It is uncommon and precious in the finer grades and has been offered as gemstone and ornamental stones for hundreds of years because of its unique tone. Recently, turquoise, like many other opaque jewels, has been devalued with access into the market of treatments, imitations and synthetics.

Formation

As a secondary mineral, turquoise is formed through the leaching impact of acidic aqueous answers for the duration of the decomposition and oxidation of pre-existing minerals. As an example, copper can also come from number one copper sulphides such as chalcopyrite or from secondary carbonates of malachite or azurite; derived from aluminum feldspar; and phosphorus from apatite. Because turquoise is regularly discovered in arid areas, generally in crammed or volcanic rocks, often in turquoise regions that fill or absorb cavities and cracks filled with related limonite and different iron oxides, weather factors play an critical role. Inside the southwestern u.s.a., turquoise is sort of continually unchanged with the decomposition merchandise of copper sulphide deposits in or round potassium-feldspar-containing porphyritic interventions. In some formations, alunite, potassium aluminum sulfate, is a distinguished secondary mineral. Typically turquoise mineralization is constrained to a shallow intensity of much less than 20 meters (66 ft), but happens at deeper fracture zones wherein the secondary solutions have greater penetration or the intensity of the water desk is greater.

Chemical Properties

Chemical Classification Phosphate minerals
Formula CuAl6(PO4)4(OH)8·4H2O
Common Impurities Fe,Ca

Name: Turquois is French and means Turkish, the original stones having come into Europe from the Iranian locality through Turkey.

Association: Kaolinite, montmorillonite, allophane, wavellite, pyrite.

Polymorphism & Series: Forms two series, with chalcosiderite, and with planerite.

Mineral Group: Turquoise group

Crystallography: Triclinic; pinacoidal. Rarely in minute crystals, usually cryptocrystalline. Massive compact, reniform,- stalactitic. In thin seams, incrustations and disseminated grains.

Turquoise Composition: A basic hydrous phosphate of aluminum, Al2 (0H)3P04- H20. Excluding CuO reported in chemical analyses of turquois, the percentages of the oxides are: A120 3 = 46.8, P2Or, = 32.6, H20 = 20.6. The mineral is colored by small amounts of copper whose role in the composition is not well understood.

Diagnostic Features: Turquois can be easily recognized by its color. It is harder than ehrysocolla, the only common mineral which it resembles.

Turquoise Uses: As a gem stone. It is always cut in round or oval forms. Much turquois is cut which is veined with the various gangue materials, and such stones are sold under the name of turquois matrix.

Turquoise Physical Properties

Crystal habit Massive, nodular
Color Bright blue, sky-blue, pale green, blue-green, turquoise-blue, apple-green, green-gray
Streak Pale greenish blue to white
Luster Sub-Vitreous, Resinous, Waxy, Dull, Earthy
Cleavage Perfect on {001}, good on {010}
Diaphaneity Transparent, Translucent, Opaque
Mohs Hardness 5 – 6
Crystal System Triclinic
Tenacity Brittle
Density 2.6 – 2.8 g/cm3 (Measured)    2.91 g/cm3 (Calculated) (Mindat.com)
Fracture Irregular/Uneven, Sub-Conchoidal
Fusibility Fusible in heated
Solubility Soluble in HCl

Occurrence of Turquoise

Turquoise become most of the first mined stones, and even though a number of them are still studied today, many historical web sites are extinct. Those are all small-scale operations; because of the limited scope and distance of deposits, they’re generally seasonal. Most manually perform with very little mechanization. However, turquoise is often recycled as a of massive-scale copper mining operations, particularly within the United States of America.

Iran: Iran has been vital turquoise source for at least 2,000 years. It was to begin with called “pērōzah” by the Iranians, meaning “victory”, after which the Arabs were known as “fayrūzah”, which changed into mentioned “fīrūzeh” in contemporary Persian. In Iranian structure, blue turned into used to cover the domes of turquoise palaces, due to the fact the intense blue colour changed into additionally a symbol of heaven on earth.

Sinai: as a minimum the primary Dynasty (BCE 3000) in historical Egypt, and probably earlier than it, turned into utilized by the turquoise Egyptians and became extracted by means of them in the Sinai Peninsula. This vicinity turned into regarded by the local Monitu as the Turquoise use. There are six mines at the southwest coast of the peninsula, overlaying an area of ​​approximately 650 rectangular kilometers (250 square meters). The maximum vital of these mines are Serabit al-Khadim and Wadi Maghareh, traditionally believed to be one of the oldest known mines. The historic mine is ready four kilometers from an historical temple devoted to the gods Hathor.

USA: The Southwest United States is a crucial turquoise supply; Arizona, California (San Bernardino, Imperial, Inyo counties), Colorado (Conejos, El Paso, Lake, Saguache counties), New Mexico (Eddy, grant, Otero, Santa Fe counties) and Nevada (Clark, Elko, Esmeralda County, Eureka) Lander, Mineral County and Nye counties). California and New Mexico’s deposits had been extracted by way of native individuals, pre-Columbian, using stone equipment, a few nearby and a few as far flung as valuable Mexico. Cerrillos is notion to be the website of the oldest mines in New Mexico; before the Nineteen Twenties the country was the USA’s largest producer; extra or much less exhausted today. A mine positioned within the Apache Canyon in California is currently in industrial ability.

Different Sources: Turquoise prehistoric artifacts (beads) had been regarded from BCE’s regions inside the Japanese Rhodopes in Bulgaria for the fifth millennium – the supply of uncooked materials is probably associated with the close by Spahievo lead-zinc ore field.

China has been a small turquoise supply for extra than 3000 years. The jewel-great fabric inside the shape of compact nodules is observed inside the damaged, silicified limestones of Yunxian and Zhushan in Hubei province. Further, Marco Polo pronounced the presence of turquoise in contemporary Sichuan. Maximum Chinese materials are exported, but there are numerous carvings carved like jade. In Tibet, the Derge and Nagari-Khorsum mountains in the east and west of the place are claimed to have jewel-first-rate deposits.

Different noteworthy places are: Afghanistan; Australia (Victoria and Queensland); North India; Northern Chile (Chuquicamata); Cornwall; Saxony; Silesia; and Turkestan.

Turquoise Optical Properties

Color / Pleochroism Weak X= colorless Z= pale blue or pale green
2V: Measured: 40° , Calculated: 44°
RI values: nα = 1.610 nβ = 1.615 nγ = 1.650
Optic Sign Biaxial (+)
Birefringence 0.040
Relief Moderate
Dispersion: r < v strong

Distribution

Dozens of localities, of which only a few can be mentioned, for commercial amounts or good crystals.

  • In Iran, at Madan, 45 km northwest of Neyshabur (Nishapur).
  • From Ottre, near Vielsalm, Belgium.
  • At the Bunny mine, St. Austell, and elsewhere in Cornwall, England.
  • From Katonto, north of Kolwezi, Katanga Province, Congo (Shaba Province, Zaire), good crystals.
  • In the USA, crystallized from the Bishop mine, Lynch Station, Campbell Co., Virginia; in the Cerrillos district, Santa Fe Co., and the Burro Mountains district, Grant Co., New Mexico; in Arizona, commercial production from Mineral Park, Mohave Co., Morenci, Greenlee Co., the Globe-Miami district, Gila Co., and others; numerous small deposits in Lander Co. and elsewhere in Nevada.
  • In the Itatiaiucu iron mine, southwest of Belo Horizonte, Minas Gerais, Brazil, large crystals.
  • At Chuquicamata, Antofagasta, Chile.
  • In Australia, at Narooma, New South Wales, as crystals; in the Iron Monarch quarry, Iron Knob, South Australia.
  • In China, from Yunxian and Zhushan, Wudang Mountains, Hubei Province, and near Shanyang, Shaanxi Province.

References

  • Bonewitz, R. (2012). Rocks and minerals. 2nd ed. London: DK Publishing.
  • Dana, J. D. (1864). Manual of Mineralogy… Wiley.
  • Handbookofmineralogy.org. (2019). Handbook of Mineralogy. [online] Available at: http://www.handbookofmineralogy.org [Accessed 4 Mar. 2019].
  • Mindat.org. (2019): Mineral information, data and localities.. [online] Available at: https://www.mindat.org/ [Accessed. 2019].
  • Wikipedia contributors. (2019, June 25). Turquoise. In Wikipedia, The Free Encyclopedia. Retrieved 02:25, July 9, 2019, from https://en.wikipedia.org/w/index.php?title=Turquoise&oldid=903470553
Cite this article as: Geology Science. (2019). Turquoise. [online] Available at: http://geologyscience.com/gemstone/turquoise/ [21st October 2019 ]
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