Cornubite - Encyclopedia
Class : Phosphates, arsenates, vanadates
Subclass : Anhydrous arsenates
Crystal system : Triclinic
Chemistry : Cu5(AsO4)2(OH)4
Rarity : Rare
Cornubite is a rare arsenate from the oxidation zone of copper deposits, it is dimorphic with cornwallite. It takes its name from the Roman appellation of Cornwall : Cornubia, its region of discovery. It is a mineral which rarely forms small tabular crystals not exceeding 5 mm, and ordinarily occurs in fibrous, botryoidal to globular masses, sometimes with a porcelain-like appearance, accompanied by numerous other secondary copper minerals (malachite, olivenite...). Cornubite comes in different shades of green.
Main photo : Cornubite and azurite from Cap Garonne, Var, France © Stephan Wolfsried
Cornubite in the World
Twinning
No twin known for this mineral species.
Fakes and treatments
No fake identified for this mineral species but can be difficult to differentiate from the malachite with which it shares its deposits.
Hardness : 4
Density : 4.64
Fracture : Irregular to sub-conchoidal
Streak : Pale green
TP : Transparent to translucent
RI : 1.870 to 1.900
Birefringence : 0.030
Optical character : Biaxial -
Pleochroism : None
Fluorescence : None
Solubility : -
Magnetism : None
Radioactivity : None