Cornwallite

Cornwallite is an uncommon copper arsenate mineral with formula Cu5(AsO4)2(OH)4.

It forms a series with the phosphate pseudomalachite and is a dimorph of the triclinic cornubite.

It is a green monoclinic mineral which forms as radial to fibrous encrustations.

[4] It occurs as secondary mineral in the oxidized zone of copper sulfide deposits.

Associated minerals include olivenite, cornubite, arthurite, clinoclase, chalcophyllite, strashimirite, lavendulan, tyrolite, spangolite, austinite, conichalcite, brochantite, azurite and malachite.

Botryoidal, green cornwallite in a gossan with white baryte from Caldbeck Fells , Cumbria (7.6 × 5.1 × 4.7 cm)