CORNUBITE

    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

Cornubite is relatively common in the gossans of the copper veins of English Cornwall (Gwennap, Gwinear, Linkinhorne...), and in that of Caldbeck Fells in Cumbria. It is found in the surface areas of American copper deposits, notably those of Utah (Gold Hill, Eureka), Nevada (Majuba Hill) and Arizona (Patagonia). Cornubite is also present at the top of polymetallic veins in the Black Forest in Germany (Clara, Neubulach, etc...).

Photo on the right : Cornubite from Clara Mine, Germany © Michael Förch

Cornubite in France

In France, cornubite is present at Cap Garonne (Var), at Col de Roua near Daluis (Alpes-Maritimes), at Faymont (Vosges), at Salsigne (Aude) and at Ste-Marie-aux-Mines (Haut-Rhin).

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

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