Tungstates and Phosphates: Turquois
(including Arsenates and Vanadates)

Composition: CuAl₆(PO₄)₄(OH)₈.4H₂0

Crystal system: Triclinic; usually massive, also concretionary, stalactitic and earthy forms

8.6.1
turquois jewellery

Properties:

• Vitreous to greasy lustre
• Blue to green color
• White to pale green streak
• Knife barely scratches or not at all (Mohs' Hardness 5-6)
• Average density
• Cleavage rarely obvious
• Smooth fracture
• Not ferromagnetic
• Does not react with hydrochloric acid (HCl)

Occurrence:

Turquois occurs with limonite, chalcedony and clays in secondary deposits formed where copper-bearing surface waters have reacted with aluminous igneous or sedimentary rocks.

8.6.2
turquois jewellery

Strongly colored massive varieties of turquois are used for ornamental purposes.