DUMONTITE

    Class : Phosphates, arsenates, vanadates
    Subclass : Uranyl phosphates
    Crystal system : Monoclinic
    Chemistry : Pb2(UO2)3O2(PO4)2 5H2O
    Rarity : Very rare

Dumontite is an extremely rare lead and uranium phosphate present in the oxidation zone of uranium deposits. Its name was given to it in honor of the Belgian geologist André Hubert Dumont. It occurs in elongated lamellar crystals, not exceeding 1.5 mm, sometimes united in star-shaped aggregates, of a pale yellow to golden yellow color.

Main photo : Dumontite from Echassières, Allier, France © Michael Förch

Dumontite from Green Monster Mine, Nevada, USA © Elmar Lackner
Dumontite from Shinkolobwe, Democratic Republic of Congo © Stephan Wolfsried
Dumontite from Shinkolobwe, Democratic Republic of Congo © Italo Campostrini
Dumontite from Shinkolobwe, Democratic Republic of Congo © Uwe Haubenreisser

Dumontite in the World

The best specimens of dumontite come from Shinkolobwe (Katanga, Democratic Republic of Congo), where the crystals fill voids in the torbernite. Dumontite is also reported at Kobokobo, still in Congo and in the American deposits of Nogales and Goodsprings (Nevada). It is also found in Jabiru and Saddle Ridge in the Australian Northern Territories.

Dumontite in France

In France, dumontite is reported at Echassières (Allier) in pretty millimeter crystals.

Twinning

No twin known for this mineral species.

Fakes and treatments

No fake listed for this mineral species.


Hardness : -
Density : 5.65
Fracture : Undetermined
Streak : Yellow

TP : Translucent
RI : 1.850 to 1.890
Birefringence : 0.040
Optical character : Biaxial +
Pleochroism : Visible
Fluorescence : Green

Solubility : Acids


Magnetism : None
Radioactivity : Strong