Calcurmolite - Encyclopedia

    Class : Sulfates, chromates, molybdates
    Subclass : Uranyl molybdates
    Crystal system : Monoclinic
    Chemistry : Ca(UO2)3(MoO4)3(OH)2 11H2O
    Rarity : Very rare

Calcurmolite is an extremely rare uranium and calcium molybdate from the oxidation zone of uranium deposits. It is formed by alteration of uraninite which it can pseudomorph, and concretizes the attraction of molybdenum and uranium for the organic matter present in sedimentary deposits. Note that, unlike vanadium, molybdenum only forms very rare supergene minerals with uranium ; only nine species are known to date. It owes its name to its chemical composition (calcium + uranium + molybdenum). Calcurmolite forms coatings, prismatic crystals, lamellar or rarely spherolitic aggregates, lemon yellow in color.

Main photo : Calcurmolite from Rabejac, Hérault, France © Leon Hupperichs

Calcurmolite from Mas d’Alary, Hérault, France © Yannick Vessely
Calcurmolite from Majerská valley U, Slovakia © Martin Stevko
Calcurmolite from Rabejac, Hérault, France © Joy Desor
Calcurmolite from Majerská valley U, Slovakia © Martin Stevko

Calcurmolite in the World

Calcurmolite was discovered in a uranium and molybdenum deposit in the former USSR. Beautiful millimetric fibrous crystals are found in Majerská valley U (Slovakia).

Calcurmolite in France

Calcurmolite is present at Rabejac and Mas d'Alary in the Lodève uranium basin (Hérault) where it forms magnificent spherolitic aggregates with fibroradiated textures reaching 1 mm in diameter.


No twin known for this mineral species.

Fakes and treatments

No fake identified for this mineral species.

Hardness : 2 to 3
Density : -
Fracture : Irregular
Streak : Yellow

TP : Translucent
RI : 1.770 to 1.863
Birefringence : 0,088
Optical character : Biaxial -
Pleochroism : Visible
Fluorescence : Yellow-green

Solubility : -

Magnetism : None
Radioactivity : Strong