Bismutite - Encyclopedia

    Class : Carbonates, Nitrates, Borates
    Subclass : Anhydrous carbonates
    Crystal System : Tetragonal
    Chemistry : Bi2O2(CO3)
    Rarity : Fairly common

Bismutite is the usual supergene alteration mineral of native bismuth and bismuthinite. It is found in the oxidation zone of hydrothermal deposits containing bismuth, in particular epithermal gold deposits and polymetallic veins of the "Ni-Co-Bi-Ag-U" type, sometimes in pegmatites. Its name refers to its chemical composition : bismuth. Crystals are very rare, bismutite essentially constitutes powdery masses or spheroidal aggregates with an earthy break, medium to dark gray or olive brown, rarely white to pale yellow. Its identification is possible thanks to its cold effervescence in acids and its high density (8.1 to 8.3).

Main photo : Bismutite from Clara Mine, Baden-Württemberg, Germany © Michael Förch

Bismutite from Hohenstein, Hesse, Germany © Uwe Haubenreisser
Bismutite from Königswart Mine, Baden-Württemberg, Germany © G. Franz Zöll
Bismutite from Bergweg, Hesse, Germany © Volker Betz
Bismutite from Montroc, Tarn, France © Pascal Chollet

Bismutite in the World

The most spectacular specimens of bismutite come from the pegmatites of Ampangabé (Madagascar) : these are pseudomorphs weighing several kilos of bismuthinite crystals. The Pilgrim's Rest deposit (South Africa) yielded beautiful 5 mm crystals gathered in bushy aggregates. Good samples have been discovered in Johanngeorgenstadt (Germany) and Beresovsk (Urals, Russia), as well as in numerous American deposits.

Bismutite in France

In France, bismutite is reported in the superficial part of the bismuth veins of Meymac (Corrèze), it is also found in Puy-les-Vignes (Haute-Vienne), in Brézouard (Haut-Rhin) in emplectite pseudomorphs, in Echassières (Allier) and in many other localities.

Twinning and special crystallizations

No twin known for this mineral species.

Fakes and treatments

No fake identify for this mineral species.

Hardness : 2.5 to 3.5
Density : 6.7 to 7.4
Fracture : Irregular
Trace : Gray

TP : Translucent to transparent
RI : 2.120 to 2.300
Birefringence : 0.130 to 0.160
Optical character : Uniaxial
Pleochroism : Visible
Fluorescence : None

Solubility : Acids

Magnetism : None
Radioactivity : None