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 in the World
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