Bismutite

Bismutite
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]

The term bismuthite has been used in the past for bismuthinite.^[5]

References

1. Webmineral
2. Mindat
3. Handbook of mineralogy
4. Grice, Joel D., A Solution to the Crystal Structures of Bismutite and Beyerite, The Canadian Mineralogist, Vol. 40, pp. 693-698 (2002)
5.  Chisholm, Hugh, ed. (1911). "Bismuthite". Encyclopædia Britannica 4 (11th ed.). Cambridge University Press. p. 11.