Chalcanthite

minerals

antlerite

brochantite

chalcopyrite

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Formula: Cu(SO4).5H2O Hydrated normal sulphate
Specific gravity: 2.2 to 2.3
Hardness: 2½
Streak: Blue
Colour: Blue
Solubility: Readily soluble in water, hydrochloric, sulphuric and nitric acid
Common impurities: Fe,Mg,Co
Environments:

Hydrothermal environments

Chalcanthite is a secondary mineral that is found in the oxidation zone of copper deposits. It forms only in conditions of low pH (very acid) and high sulphate concentration, which occur only in exceptionally arid conditions; normally copper and sulphate ions remain in solution. Chalcanthite is formed by the oxidation of chalcopyrite and other copper sulphates. It is often found as a post-mining deposit on mine walls, where it crystallises from mine waters. When the carbonate concentration is similar to the atmospheric value, at successively higher values of pH (more alkaline conditions), chalcanthite is replaced by antlerite then brochantite then malachite (JRS 18.12, 13).

Alteration

chalcanthite (s) and Cu2+ (aq) to antlerite (s), H+ (aq) and H2O(l)
CuSO4.5H2O + 2Cu2+ ⇌ Cu3SO4(OH)4 + 4H+ + H2O
(MM 52.683)

The Activity-pH diagram below was calculated at 298.2 K for some arsenates and sulphates for constant activity (roughly equivalent to concentration) of H2AsO4- in solution, over a range of values of pH and of SO42- activity (MM 52.689).
stability sulphates.jpg

The mineral formulae are:
chalcanthite: Cu(SO4).5H2O
antlerite: Cu2+3(SO4)(OH)4
brochantite: Cu4(SO4)(OH)6
olivenite: Cu2(AsO4)(OH)
cornubite: Cu5(AsO4)2(OH)4
clinoclase: Cu3(AsO4)(OH)3













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