Bismutite

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.^[3] It crystallizes in the orthorhombic system and typically occurs as earthy to fibrous masses.^[2]

Bismutite
Bismutite from Schneeberg, Germany
General
Category	Carbonate mineral
Formula (repeating unit)	Bi2(CO3)O2
IMA symbol	Bit[1]
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	[2][3][4][5]

It was first described in 1841 for an occurrence in Saxony.^[2]

The term bismuthite has been used in the past for bismuthinite.^[6]

References

1. Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi:10.1180/mgm.2021.43. S2CID 235729616.
2. Webmineral
3. Mindat
4. Handbook of mineralogy
5. Grice, Joel D., A Solution to the Crystal Structures of Bismutite and Beyerite, The Canadian Mineralogist, Vol. 40, pp. 693–698 (2002)
6. Chisholm, Hugh, ed. (1911). "Bismuthite" . Encyclopædia Britannica. Vol. 4 (11th ed.). Cambridge University Press. p. 11.

See also

• Bismuthinite
• Bismoclite
• Bismite
• Eulytine
• Zavaritskite