Cornetite

Formula: Cu3(PO4)(OH)3
Anhydrous phosphate containing hydroxyl
Specific gravity: 4.10
Hardness: 4.10
Colour: Dark blue to green-blue; green-blue in transmitted light.
Solubility: Soluble in cold hydrochloric acid
Environments:

Hydrothermal environments

Cornetite is a secondary mineral in the oxidised zone of some hydrothermal copper deposits, associated with copper, brochantite, pseudomalachite, libethenite, malachite, atacamite, chrysocolla and heterogenite.

At the Desolation Prospect, Queensland, Australia, cornetite is very rare, but has been found associated with pseudomalachite and chrysocolla.

At the type locality, L'Etoile du Congo mine, Democratic Republic of the Congo, cornetite occurs in fine-grained argillaceous sandstone associated with pseudomalachite.

Common impurities: Fe,Mg,Al,Si,As,Co