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.

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.

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