The following information is from webstie: http://en.wikipedia.org/wiki/Turquoise
Turquoise is an opaque, blue-to-green mineral that is a hydrousphosphate of copper and aluminium, with the chemical formulaCuAl6(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.
The substance has been known by many names, but the word turquoise was derived around the 16th century from the French languageturquie, for Central Asian[4] material which was early imported through Turkey.
The hardness (Mohs scale) : 5 - 6
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