Bismoclite

Bismoclite
	Yellow-orange bismoclite on bismuthinite from the Alto do Giz pegmatite, Equador, Rio Grande do Norte, NE-region, Brazil. Approximate size: 20 x 6 x 2 mm.
General
Category	Halide mineral
Formula; (repeating unit)	BiOCl
Strunz classification	3.DC.25
Dana classification	10.2.1.2
Crystal system	Tetragonal
Crystal class	Ditetragonal dipyramidal (4/mmm) ; H-M symbol: (4/m 2/m 2/m)
Space group	P4/nmm
Unit cell	a = 3.887 Å, ; c = 7.354 Å; Z = 2
Identification
Color	Cream-white, greyish, yellowish brown
Crystal habit	Platey to thin rectangular crystals, fibrous to columnar, massive
Cleavage	{001} perfect
Tenacity	Elastic
Mohs scale hardness	2-2.5
Luster	Greasy, silky, pearly, dull, earthy
Streak	White
Diaphaneity	Transparent to translucent
Specific gravity	7.36 (measured), 7.784 (calculated)
Optical properties	Uniaxial (-)
Refractive index	nω = 2.150 nε = 1.910
Birefringence	δ = 0.240
References	[1][2][3][4]

Bismoclite is a bismuth oxohalide mineral with formula BiOCl. It is the naturally occurring form of bismuth oxychloride. The name was derived from its chemical constituents. It is a secondary bismuth mineral first thought to be composed of bismuthyl ions (BiO⁺) and chloride anions, however, the existence of the diatomic bismuthyl ion is doubtful.[5] It is a member of the matlockite group.

It was first described in 1935 from alluvium near bismuth-bearing pegmatites in South Africa.[2] It has been found in association with granite pegmatite and in greisen. Associated minerals include bismutite, mica, jarosite, alunite, cerussite, atacamite, connellite. Occurrences include the type locality at Jackals Water, SW of Prieska, South Africa; Bygoo, Australia; the Tintic district in the East Tintic Mountains of Utah; and from Dalbeattie, Scotland.[3]

Crystal structure

The crystal structure of bismoclite was found to be composed of linked decahedrons, specifically a square antiprism.[6] These decahedrons consist of 2 squares with sides of 3.487 Å (O-O-O-O and Cl-Cl-Cl-Cl) connected by 8 isosceles triangles (O-Cl-O and Cl-O-Cl), with a bismuth atom at the centre.[6] The Bi-O distances and Bi-Cl distances are 2.316 Å and 3.059 Å, respectively. The O-Cl distances in the triangles are 3.249 Å. The decahedrons are linked to each other through shared O-Cl sides.[6]

References

Mineralienatlas
Bismoclite on Mindat.org
Bismoclite in the Handbook of Mineralogy
Bismoclite data on Webmineral
Nils., Wiberg; 1859-, Holleman, A. F. (Arnold Frederick) (2001-01-01). Inorganic chemistry. Academic Press. ISBN 0123526515. OCLC 48056955.CS1 maint: numeric names: authors list (link)
Keramidas, Κ. G.; Voutsas, G. P.; Rentzeperis, P. I. (1993-08-01). "The crystal structure of BiOCl". Zeitschrift für Kristallographie - Crystalline Materials. 205 (1–2): 35. Bibcode:1993ZK....205...35K. doi:10.1524/zkri.1993.205.12.35. ISSN 2196-7105.

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[1] Mineralienatlas

[Mindat-2] Bismoclite on Mindat.org

[HBM-3] Bismoclite in the Handbook of Mineralogy

[Webmin-4] Bismoclite data on Webmineral

[5] Nils., Wiberg; 1859-, Holleman, A. F. (Arnold Frederick) (2001-01-01). Inorganic chemistry. Academic Press. ISBN 0123526515. OCLC 48056955.CS1 maint: numeric names: authors list (link)

[:0-6] Keramidas, Κ. G.; Voutsas, G. P.; Rentzeperis, P. I. (1993-08-01). "The crystal structure of BiOCl". Zeitschrift für Kristallographie - Crystalline Materials. 205 (1–2): 35. Bibcode:1993ZK....205...35K. doi:10.1524/zkri.1993.205.12.35. ISSN 2196-7105.