Turquoise

copper

Formula: CuAl6(PO4)4(OH)8.4H2O
Hydrated phosphate containing hydroxyl
There is nearly always some replacement of Al3+ by Fe3+, forming a partial solid solution with chalcosiderite.
Specific gravity: 2.6 to 2.9
Hardness: 5 to 6
Streak: White
Colour: Azure-blue to apple-green
Solubility: Slightly soluble in hydrochloric acid
Environments:

Sedimentary environments

Turquoise is a secondary mineral deposited by copper-bearing hydrothermal waters or meteoric waters containing dissolved copper (R&M 87.4.333). It is usually found in small veins in decomposed volcanic rocks in arid regions. It accumulates in crevices, particularly in trachyte, slate and sandstone.

At the Mount Lofty ranges, South Australia, turquoise is found at the Moculta quarry associated with apatite and jarosite. At the Fairview workings it is associated with wavellite and fluellite (AJM 17.1.26).

Common impurities: Fe,Ca

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