Carnotite - Encyclopedia

    Class : Phosphates, arsenates, vanadates
    Subclass : Uranyl vanadate
    Crystal system : Monoclinic
    Chemistry : K2(UO2)2(VO4)2 3H2O
    Rarity : Quite common

Carnotite is a fairly common secondary mineral in the oxidation zone of uranium deposits in sedimentary contexts. It owes its name to the French chemist and mining engineer Marie-Adolphe Carnot. It is a hydrated vanadate of uranium and potassium which most often occurs in crystalline powder, or in inconsistent microcrystalline aggregates, lemon yellow to amber yellow in color. More rarely, it forms flattened crystals, associated in divergent aggregates. It constitutes the main uranium ore in the sedimentary deposits of Colorado (Uravan, Placerville, Paradox, etc...).

Main photo : Carnotite from Monument Valley, Utah, USA © Stephan Wolfsried

Carnotite from Mashamba West Mine, Katanga, Congo © Uwe Haubenreisser
Carnotite from Anderson Mine, Arizona, USA © Stephan Wolfsried
Carnotite from Clara Mine, Germany © Michael Förch
Carnotite from Anderson Mine, Arizona, USA © Pascale & Daniel Journet

Carnotite in the World

The sedimentary deposits of Colorado have sometimes provided superb crystallizations. In Arizona, carnotite is also very abundant in the Monument Valley mines, where it is exploited as a dual ore of vanadium and uranium. Also in Arizona, the Anderson mine yielded beautiful millimeter crystals. Excellent millimeter crystals, some of the best known, come from the Mashamba mines in Katanga (Congo).

Carnotite in France

In France, carnotite is known in Echassières (Allier), Autun (Saône-et-Loire), Meilhac (Haute-Vienne) and Rabejac (Hérault).

Twinning and special crystallizations

twin is known on {001}.

Due to its origin in a sedimentary context, carnotite can cover certain fossils, this is the case in Cameron (Arizona, USA) where specimens of carnotite were discovered on fossil wood.

Right photo : Carnotite on fossil wood from Cameron, Arizona, USA @ Kelly Nash

Fakes and treatments

No fake identified for this mineral species.

Hardness : 2
Density : 4.70
Fracture : Micaceous
Streak : Yellow

TP : Translucent
RI : 1.750 to 1.950
Birefringence : 0.200
Optical character : Biaxial -
Pleochroism : Low
Fluorescence : None

Solubility : Acids

Magnetism : None
Radioactivity : Very strong


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