Bismutite

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Bismutite
Bismutit (Wismutcarbonat) - Schneeberg, Erzgebirge.jpg
Bismutite from Schneeberg, Germany
General
Category Carbonate mineral
Formula
(repeating unit)
Bi2(CO3)O2
Strunz classification 05.BE.25
Dana classification 16a.03.05.01
Crystal symmetry Orthorhombic mm2 - pyramidal
Unit cell a = 3.865Å, b = 3.862Å, c = 13.675Å; 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
Crystal system Orthorhombic
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 [1][2][3][4]

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.[2] It crystallizes in the orthorhombic system and typically occurs as earthy to fibrous masses.[1]

It was first described in 1841 for an occurrence in Saxony.[1]

References[edit]