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Formula: CuAl4(SO4)(OH)12.3H2O
Crystal System: Monoclinic
Hydrated sulphate containing hydroxyl
Specific gravity: 2.29 measured, 2.25 calculated
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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