Rocks, Minerals & Ores
Metallic Oxides
Turquoise
copper aluminum phosphateLane Mountain, Barstow, CA
Hydrous copper aluminum phosphate
Chemical formula: CuAl6(PO4)4(OH)8·4H2O
near Barstow, California
Turquoise is an opaque blue to blue-green phosphate mineral containing copper and aluminum. It forms as a secondary mineral near the surface, where groundwater moves through copper-bearing, aluminum-rich rock. The mineral commonly fills fractures or occurs as thin veins, nodules, and irregular crusts.
Copper produces turquoise’s characteristic blue color. Iron substituting within its mineral structure can contribute green or yellow-green shades. Brown or black markings within a specimen generally consist of remnants of the surrounding host rock, commonly called matrix.
Turquoise has a Mohs hardness of approximately 5 to 6 and typically displays a waxy to subvitreous luster. Dense material takes a good polish and has been used for jewelry and ornament for thousands of years.
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Metallic Oxides
Royston Mine, Tonopah, NV
Halloran, Baker, CA
Halloran Turqouise