Composition and structure of Chalcosiderite and Turquoise

Turquoise: CuAl6(PO4)4(OH)8:4H20

Chalcosiderite: CuFe6(PO4)4(OH)8:4H20

Composition, Structure and Associated Minerals:

There is a complete solution which exists between Chalcosiderite, CuFe6 (PO4)4 (OH)8:4H2O, and turquoise CuAl6 (PO4)4 (OH)8:4H2O. Because of this, aluminum may partly substitute for iron in the mineral's crystal structure. In places like Lander County Nevada, Chalcosiderite and turquoise also occur together in the same general area.

Identification and Diagnostics

Gives a positive test for copper, iron and phosphates, but exact determinations between turquoise and chalcosiderite may require a chemical analysis of the mineral make up.

Occurrence, Localities and Origins:

A rare copper-iron secondary phosphate. It occurs only in a few places in the US, where it is associated with the oxidized zones of some copper deposits. In Lander County, Nevada it occurs at the Damale mine where it is found as emerald green nodules in association with variscite and faustite. It is also found at the Lander Ranch mine near Tenabo. The photos pictured here are the Lander Ranch material.

Finds of chalcosiderite in which it appears similar to turquoise has lead to the mineral being used as a gemstone in a manner similar to turquoise. It's attractive colors and spider web patters have increased its popularity.