Antlerite

antlerite

chalcanthite

cuprite

brochantite

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Formula: Cu²⁺₃(SO₄)(OH)₄
Anhydrous sulphate containing hydroxyl
Pseudomorphs of cuprite after fibrous antlerite have been observed
Crystal System: Orthorhombic
Specific gravity: 3.88 measured, 3.93 calculated
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

The Two Mile and Three Mile deposits, Paddy's River, Paddys River District, Australian Capital Territory, Australia, are skarn deposits at the contact between granodiorite and volcanic rocks. antlerite is a secondary sulphate that occurs with brochantite in sulphide-bearning magnetite skarn (AJM 22.1.43).

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 SO₄^2- activity (MM 52.689).


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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