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
Colour: Azure-blue to apple-green
Solubility: Slightly soluble in hydrochloric acid
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
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).
At the Mount Deverell variscite deposit, Milgun Station, Western Australia, turquoise occurs in altered variscite associated with wardite and millisite. The variscite deposits are hosted by marine sedimentary rocks (AJM 20.2.31).
At Nacozari, Mexico, turquoise pseudomorphs after apatite have been found (KL p211).
Common impurities: Fe,Ca
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