Chalcoalumite

chalcoalumite

cuprite

gibbsite

mbobomkulite

Images

Formula: CuAl4(SO4)(OH)12.3H2O
Hydrated sulphate containing hydroxyl
Specific gravity: 2.29
Hardness: 2½
Streak: White
Colour: Turquoise-green, pale blue, bluish grey, colourless in transmitted light
Solubility: Slowly soluble in cold dilute acids
Environments

Sedimentary environments
Hydrothermal environments

Chalcoalumite is a rare secondary mineral in the oxidised portions of copper deposits (Webmin). It alters to cuprian gibbsite (Dana).

Localities

At the Mbobo Mkulu Cave, Mbombela, Ehlanzeni District, Mpumalanga, South Africa, chalcoalumite is associated with mbobomkulite and hydrombobomkulite (HOM).

At the type locality, the Holbrook mine, Copper Queen Mine, Queen Hill, Bisbee, Cochise County, Arizona, USA, chalcoalumite forms crusts from one to ten millimeters thick on a brown limonite-like material. Malachite and azurite were deposited on the limonite before the chalcoalumite. Some of the specimens are stalactites of limonite completely covered with a layer of chalcoalumite (AM 10.79-83). Other associates include cuprite and goethite (HOM).

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