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Bismutite

Bismutite
Bismutit (Wismutcarbonat) - Schneeberg, Erzgebirge.jpg
Bismutite from Schneeberg, Germany
General
Category Carbonate mineral
Formula
(repeating unit)
Bi2(CO3)O2
Strunz classification 5.BE.25
Dana classification 16a.03.05.01
Crystal system Orthorhombic
Crystal class Pyramidal (mm2)
(same H-M symbol)
Space group Immm
Unit cell a = 3.865 Å, b = 3.862 Å,
c = 13.675 Å; Z = 2
Identification
Color Yellow to brown, greenish, green-grey, grey or black
Crystal habit Very rare as platy crystals; typically radially fibrous to spheroidal, in crusts and earthy to dense massive aggregates
Twinning pseudo-merohedral twinning simulates tetragonal symmetry
Cleavage Distinct/Good on {001} (microscopically observable)
Mohs scale hardness 2.5 - 3.5
Luster Vitreous, waxy, may be dull to earthy
Streak Grey
Diaphaneity Opaque to transparent in small grains
Specific gravity 6.7 - 7.4 measured, 8.15 calculated
Optical properties Biaxial (-) (appears uniaxial due to twinning)
Refractive index a=2.12-2.15, b=2.12-2.15, g=2.28
Birefringence 0.1300-0.1600
2V angle 45
References

Bismutite or bismuthite is a bismuth carbonate mineral with formula Bi2(CO3)O2 (bismuth subcarbonate). Bismutite occurs as an oxidation product of other bismuth minerals such as bismuthinite and native bismuth in hydrothermal veins and pegmatites. It crystallizes in the orthorhombic system and typically occurs as earthy to fibrous masses.

It was first described in 1841 for an occurrence in Saxony.

The term bismuthite has been used in the past for bismuthinite.



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