Guilleminite - Encyclopedia

    Class : Oxides and hydroxides
    Subclass : Uranyl selenites
    Crystal system : Orthorhombic
    Chemistry : Ba(UO2)3(SeO3)2O2 3H2O
    Rarity : Very rare


The appearance of guilleminite and other uranium selenites requires the joint presence of sufficient quantities of selenium and uranium in the same deposit. These conditions are only exceptionally met, which explains the great rarity of these minerals, only 4 in number (guilleminite, demesmaekerite, derriksite, marthozite), and their presence in rare deposits. It was named in honor of Claude Guillemin, mineralogist and co-founder of the BRGM and the IMA. Guilleminite forms tabular crystals of rectangular habit not exceeding 0.4 mm in geodic voids, as well as coatings and small fibrous clusters reaching 1 cm in diameter. Its color is canary yellow.

Main photo : Guilleminite du Liauzun, Olloix, Puy-de-Dôme, France © Thierry Lesenechal

Guilleminite and malachite from Musonoï, Kolwezi, D.R. Congo © Uwe Haubenreisser
Guilleminite and malachite from Musonoï, Kolwezi, D. R. Congo © Chuck Adan
Guilleminite & vandenbrandeite from Musonoï, Kolwezi, R. D. Congo © Stephan Wolfsried
Guilleminite & vandenbrandeite from Musonoï, Kolwezi, R. D. Congo © Elmar Lackner

Guilleminite in the World

Guilleminite appears in the oxidation zone of the Musonoi deposit. Uranium comes from the oxidation of pitchblende, selenium from the alteration of a seleniferous digenite. This digenite then appears covered with microcrystalline coatings of guilleminite, derriksite and demesmaekerite.

Guilleminite in France

In France, guilleminite is reported in Liauzun, near Olloix (Puy-de-Dôme).

Twinning

No twin known for this mineral species.

Fakes and treatments

No fakes recorded for this mineral species.



Hardness : 2
Density : 4.88
Fracture : Undetermined
Streak : Light yellow


TP : Translucent
RI : 1.720 to 1.805
Birefringence : 0.085
Optical character : Biaxial -
Pleochroism : Strong
Fluorescence : None


Solubility : -

Magnetism : NoneRadioactivity : Very strong

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