Rocks, Minerals & Ores
Metallic Oxides
Turquoise
Hydrous copper aluminum phosphateChemical formula: CuAl6(PO4)4(OH)8·4H2O
Locality: Royston Mine, Royston Mining District, Nye County, Nevada
Turquoise with matrix from the Royston Mine, Royston Mining District, Nye County, Nevada.
Turquoise is a secondary phosphate mineral best known for its blue to blue-green color. It forms near the surface when copper-bearing groundwater reacts with aluminum- and phosphorus-bearing rocks. The mineral commonly occurs as veins, nodules, and crust-like fillings in altered rock.
Copper gives turquoise its characteristic blue color, while iron may contribute greener or yellow-green shades. Material from Nevada may range from clear blue to green and commonly contains brown or black host-rock matrix.
The Royston Mining District, in the Royston Hills west-northwest of Tonopah, is one of Nevada's best-known turquoise-producing areas. Its turquoise is noted for blue and green colors, frequently accompanied by a brown or golden-brown matrix. (Mindat locality record)
The opening description "copper aluminum phosphate" is not wrong, but "hydrous copper aluminum phosphate" is more precise.
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