Antlerite

antlerite

chalcanthite

cuprite

brochantite

Images

Formula: Cu2+3(SO4)(OH)4
Anhydrous sulphate containing hydroxyl
Pseudomorphs of cuprite after fibrous antlerite have been observed
Specific gravity: 3.9
Hardness: 3½
Streak: Light green
Colour: Emerald-green to blackish-green, also light green
Solubility: Soluble in dilute sulphuric acid
Environments:

Hydrothermal environments

Antlerite is a secondary mineral occurring in the oxidised zone of copper deposits in arid regions in very acid conditions. When the carbonate concentration is similar to the atmospheric value, at successively higher values of pH (less acid conditions), chalcanthite is replaced by antlerite then brochantite then malachite. Antlerite is a rare mineral, because normally in an oxidising deposit pH will be too high (too alkaline) for it to form. The walls of mines, where there is abundant pyrite, are mainly where it has been found in the UK (JRS 18.12, 13). Antlerite is metastable at ambient temperature with respect to brochantite (JRS 18.12, 13).

Localities

At Caldbeck Fells, Cumbria, England, UK, antlerite is very rare. It has been found at the Old Potts Gill mine as powdery aggregates in malachite (C&S).

At Parys Mountain, Anglesey, Wales, UK, oxidation of chalcopyrite in very low pH (highly acid) conditions has created the required environment for formation of antlerite, which occurs as a post-mining mineral in association with brochantite. Crystals are only visible under the scanning electron microscope (MW).

Alteration

antlerite and water to brochantite and and sulphuric acid
4Cu3SO4(OH)4(s) + 2H2O(l) → 3Cu4SO4(OH)6(s) + H2SO4(aq)
(JRS 18.12, 13)

chalcanthite (s) and Cu2+ (aq) to antlerite (s), H+ (aq) and H2O(l)
CuSO4.5H2 + 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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