Turquoise is an opaque mineral, most often blue-green in color, with a chemical description as a hydrated copper and aluminum phosphate, formulated as CuAl6(PO4)4(OH)8·4H2O. Colors can vary from white to powder blue, to green blue and green-yellow, depending on the concentration of copper and iron, or aluminum impurities.
Finer grades of turquoise are rare. They have been found in areas of the Southwest United States, Iran, Sinai, Bulgaria, China, Tibet, Afghanistan, Australia, India, Chile, and Turkestan.
Deposits of turquoise typically form in iron-rich limonite or sandstone. Sandstone turquoise features tan markings, while limonite showcases brown markings in the turquoise. Referred to as matrix, these markings look like veins and are left within the turquoise from the host rock.
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