Turquoise is an opaque, blue-to-green
mineral that is a
hydrated phosphate of
copper and
aluminium, with the
chemical formula CuAl6()
4(
OH)
8·4. 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.