Turquoise

turquoise, hydrous phosphate of aluminum and copper, Al₂(OH)₃PO₄·H₂O+Cu, used as a gem. It occurs rarely in crystal form, but is usually cryptocrystalline. Turquoise is opaque and has a waxy luster; the color varies from greenish gray to sky-blue. The sky-blue varieties are the most valued as gems, but because of their porosity they easily absorb dirt and grease and change in color to an unattractive green. Exposure to heat or sunlight is also injurious to the color of the turquoise. The finest specimens come from Iran; other sources are the Sinai peninsula and the SW United States, especially New Mexico, Nevada, Arizona, and Colorado. Turquoise matrix is a rock including fragments of turquoise, cut as a gem stone. Variscite, the hydrated phosphate of aluminum, is sometimes used as a substitute for turquoise. It occurs in crystals of the orthorhombic system and in massive form; minable deposits are found in Utah.

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turquoise

Hydrated copper and aluminum phosphate mineral, CuAl₆(PO₄)₄(OH)₈·4H₂O, that is used extensively as a gemstone. The colour of turquoise ranges from blue through various shades of green to greenish and yellowish gray. A delicate sky-blue, which provides an attractive contrast with precious metals, is most valued for gem purposes. Numerous deposits of turquoise in the southwestern U.S. have been worked for centuries by American Indians. The mineral also occurs in Iran, northern Africa, Australia, and Siberia.

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turquoise

1. a greenish-blue fine-grained secondary mineral consisting of hydrated copper aluminium phosphate. It occurs in igneous rocks rich in aluminium and is used as a gemstone. Formula: CuAl₆(PO₄)₄(OH)₈.4H₂O

2. the colour of turquoise

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turquoise [′tər‚kwȯiz]

(mineralogy)

CuAl₆(PO₄)₄(OH)₈·4H₂O A semitranslucent sky-blue, bluish-green, apple-green, or greenish-gray mineral that crystallizes in the triclinic system and occurs in veinlets or as crusts of massive, concretionary, and stalactite shapes; an important gem mineral. Also known as calaite; Turkey stone.

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turquoise

December. [Am. Gem Symbolism: Kunz, 319–320]

See : Birthstones

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turquoise

seeing turquoise after a new moon brings wealth. [Gem Symbolism: Kunz, 345]

See : Wealth

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Turquoise

a mineral of the chemical composition CuAl₆[P0₄]₄(OH)₈·4H₂O. It crystallizes in a tricline system. It usually forms compact, cryptocrystalline masses, kidney-shaped aggregates, incrustations, thin veins, and so on. Its hardness on the mineralogical scale is 5–6; its density is 2,600–2,800 kg/m³. The luster is dull and waxy. It is distinguished by a beautiful sky-blue or greenish-blue color. The formation of turquoise is associated with the weathering of feldspar rocks rich in Al₂O₃ and phosphates (apatite, phosphorite, and others) under the influence of surface waters that contain copper ions. Turquoise is sometimes formed by the replacement of parts of the skeleton of fossil animals (so-called odontolite). Owing to its beautiful color (particularly in polished form), it is widely used in art and jewelry items as a semiprecious stone. The largest deposit of turquoise is at Nishapur in Iran. In the USSR, turquoise is found in Middle Asia and Kazakhstan.

G. P. BARSANOV