Compreignacite - Encyclopedia
Class : Oxides and hydroxides
Subclass : Uranyl hydroxides
Crystal system : Orthorhombic
Chemistry : K2(UO2)6O4(OH)6 8H2O
Rarity : Very rare
Compreignacite was discovered in 1957 in the Margnac uranium deposit, in the town of Compreignac (Haute-Vienne, France) which gave it its name, then it was described a few years later. It constitutes one of these yellow products, gummites, which result from the transformation of uraninite when it oxidizes under the action of water and air, forming yellowish crusts on the periphery of the nodules of pitchblende. Compreignacite forms yellow crystals measuring a few tenths of a millimeter, with a parallelepiped appearance, sometimes twinned. It is the potassium analogue of billietite with which it is isostructural. It is usually found associated with uranotile, billietite and becquerelite.
Main photo : Coffinite from © L
Compreignacite in the World
Twinning
A twin is known on (110).
Fakes and treatments
No fakes recorded for this mineral species.
Hardness : Indeterminate
Density : 5.103
Fracture : Indeterminate
Streak : Light yellow
TP : Translucent to transparent
RI : 1.789 to 1.802
Birefringence : 0.013
Optical character : Biaxial -
Pleochroism : Strong
Fluorescence : Green
Solubility : -
Magnetism : None
Radioactivity : Very strong