CERULEITE

    Class : Phosphates, arsenates, vanadates
    Subclass : Hydrated arsenates
    Crystal system : Triclinic
    Chemistry : Cu2Al7(AsO4)4(OH)13 12H2O
    Rarity : Very rare

Ceruleite is a copper and aluminum arsenate from oxidized zones of arsenic-rich polymetallic deposits. It is commonly of recent formation in mine galleries. It takes its name from the Latin caeruleus (azure) because of its color. Ceruleite forms microscopic crystals, assembled into powdery encrustations, chalky concretions or spherical aggregates of up to 10 cm, pale blue to sky blue, sometimes dark blue.

Main photo : Ceruleite from Wheal Gorland, St Day, Cornwall, England, UK © Gianfranco Ciccolini

Ceruleite in the World

The best specimens of ceruleite come from English Cornwall, notably the districts of Gwennap and St-Hilary. It is also reported in Chile (Guanaco) and Tsumeb (Namibia).

Ceruleite in France

In France, ceruleite is only known from the copper mine of Cap Garonne (Var).

Right photo : Ceruleite from Cap Garonne, Var, France © Stephan Wolfsried

Twinning

No twin known for this mineral species.

Fakes and treatments

No fake identified for this mineral species.


Hardness : 5 to 6
Density : 2.70 to 2.80
Fracture : Irregular
Streak : White to pale blue

TP : Translucent
RI : 1.60
Birefringence : -
Optical character : Biaxial
Pleochroism : None
Fluorescence : None

Solubility : Hydrochloric acid and potash


Magnetism : None
Radioactivity : None