Turquoise is an opaque, blue-to-green mineral that is a hydrated phosphate of copper and aluminium, with the chemical formula CuAl6(PO4)4(OH)8ยท4H2O. It is rare and valuable in finer grades and has been prized as a gemstone and ornamental stone for thousands of years owing to its unique hue. Like most other opaque gems, turquoise has been devalued by the introduction onto the market of treatments, imitations and synthetics.
