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Turquoise is an opaque, blue-to-green mineral that is a hydrous phosphate of copper and aluminium, with the chemical formula CuAl6(PO4)4(OH)8�4H2O. It is rare and valuable in finer grades and has been prized as a gem and ornamental stone for thousands of years owing to its unique hue. In recent times, turquoise, like most other opaque gems, has been devalued by the introduction of treatments, imitations, and synthetics onto the market. (source: Wikipedia) Photo by Michael Marcotte Public domain photo below by Arpingstone turquoise from New Mexico (photo by Michael Marcotte) Return to List Back to Michael's Hobbies page Back to Michael Marcotte's HomePage