Turquoise is probably the most valuable, non-transparent mineral in the jewelry trade. It was mined by Egyptians on the Sinai Peninsula as early as 6000 BC. and was transported to Europe through Turkey, accounting for its name, which means "Turkish" in French.

Turquoise is hydrated copper and aluminum phosphate achieving hardness six  -- CuAl6(PO 4)4(OH)8 4H2O -- that is used extensively as a gemstone. It is a secondary mineral deposited from circulating waters, occurring exclusively in desert and arid environments. It appears blue to green, with waxy veins in aluminum-rich, volcanic or sedimentary rocks. The blue color is caused by copper, while the green color is caused by iron or chromium.