Cornetite - Encyclopedia

    Class : Phosphates, arsenates, vanadates
    Subclass : Anhydrous phosphates
    Crystal system : Orthorhombic
    Chemistry : Cu3PO4(OH)3
    Rarity : Rare

Cornetite is a rare secondary phosphate from the oxidation zones of copper deposits. Its genesis seems to be favored by an arid climate, as for many copper sulphates. It owes its name to the Belgian geologist Jules Cornet. Its crystals are small short prisms with rounded edges, not reaching a centimeter, of a beautiful deep blue color, frequently gathered in rosettes or encrustations. Cornetite is associated with other secondary copper minerals (malachite, chrysocolla, brochantite, etc...), and sometimes manganese. Its rarity is partly due to the fact that it is easily transformed into libethenite by loss of ions (OH). It is a mineral intended only for the collection.

Cornétite de la Mine de l'Étoile, Congo
Cornétite de la Mine de l'Étoile, Congo
Cornétite de la Mine de l'Étoile, Congo
Cornétite de la Mine de l'Étoile, Congo

Cornetite in the World

Beautiful cornetite crystals come from the deposits of Congolese Katanga, in particular from the Etoile du Congo mine, near Lubumbashi, its site of discovery (main photo and photo on the right). Beautiful specimens were also extracted from the oxidation zones of the large American copper porphyries, in particular those of Yerington (Nevada). Cornetite is also reported in deposits of the copper-belt of Zimbabwe (Karoi region), and in Chilean copper deposits (Chuquicamata, Inca de Oro, etc...).

Cornetite in France

This mineral is not reported in French underground.


A twin plane is known for the species but is very difficult to identify with the naked eye.

Fakes and scams

No fake recorded for this mineral species, it can however be confused with other blue copper minerals such as azurite.

Hardness : 4.5
Density : 4.1
Fracture : -
Trace : Blue

TP : Transparent to translucent
RI : 1.765 to 1.820
Birefringence : 0.055
Optical character : Biaxial -
Pleochroism : Difficult to observe
Fluorescence : None

Solubility : Hydrochloric acid

Magnetism : None
Radioactivity : None