CALEDONITE

    Class : Sulfates, chromates, molybdates
    Subclass : Anhydrous sulfates
    Crystal system : Orthorhombic
    Chemistry : Pb5Cu2(CO3)(SO4)3(OH)6
    Rarity : Rare

Caledonite is a rare secondary mineral from the oxidation zone of lead-copper deposits in an arid climate. It accompanies other secondary minerals of lead and copper (cerussite, anglesite, malachite, azurite, chrysocolla...). It is also found in industrial slags. Its name comes from its place of discovery, Caledonia (former name of Scotland). Rarely massive, it mainly forms elongated and strongly striated prismatic crystals according to [001], of a characteristic blue-green, rarely sky blue.

Main photo : Caledonite from Mammoth-St-Antony Mine, Arizona, USA © Carsten Slotta

Caledonite from the St-Nicolas Mine, Steinbach, Haut-Rhin, France © Thierry Brunsperger
Caledonite from Blue Bell Mine, California, USA © Stephan Wolfsried
Caledonite and quartz from Bréziès, Aveyron, France © Serge Lavarde
Caledonite from Reward Mine, California, USA © Heritage Auctions

Caledonite in the World

The most beautiful specimens of caledonite, 2 cm elongated prismatic crystals, come from the Iranian mine of Chah Millé, near Anarak, and from the American mines of Mammoth-St-Anthony (Arizona) and Reward (California) where it was relatively frequent. The lead and copper hydrothermal veins in Scotland (Leadhills, Wanlockhead) also provided good millimetric crystals, as well as the Italian Arenas deposit (Sicily).

Caledonite in France

In France, caledonite is known in Argentolle (Saône-et-Loire), Steinbach (Haut-Rhin), Bréziès and Villefranche-de-Rouergue (Aveyron), Lantignié and Longefay (Rhône) in Crozet (Loire), in the industrial scoria of Poullaouen (Finistère), Menez-Plom (Côtes-d'Armor) and Vialas (Lozère) as well as in many other small localities.

Twinning

No twin known for this mineral species.

Fakes and treatments

No fake identified for this mineral species.


Hardness : 2.5 to 3
Density : 5.75
Fracture : Irregular
Streak : Blue-green to bluish white

TP : Translucent to transparent
RI : 1.818 to 1.909
Birefringence : 0.091
Optical character : Biaxial -
Pleochroism : Low
Fluorescence : None

Solubility : Nitric acid


Magnetism : None
Radioactivity : None