Which mineral is the main component of the gemstone turquoise?

Turquoise is the main component of the gemstone turquoise. It is a hydrated copper and aluminium phosphate with the formula CuAl₆(PO₄)₄(OH)₈·4H₂O, and its blue-to-green color is chiefly associated with copper and variations in composition.

Turquoise forms in arid regions where acidic, copper-bearing groundwater interacts with aluminium- and phosphate-rich rocks. It often occurs as fine-grained masses or fills fractures rather than forming large transparent crystals. Iron can shift its color toward green, while a dark matrix of host rock may remain visible in the finished stone.

The gemstone has been valued for thousands of years, including in ancient Egypt and Persia. Turquoise is softer and more porous than many transparent gems, so heat, chemicals, and prolonged moisture can damage or discolor it. Malachite and azurite are also copper minerals, but their compositions and typical colors differ.