Bismoclite

Bismoclite
General
Category	Halide mineral - Oxide mineral
Formula (repeating unit)	BiOCl
Strunz classification	3.DC.25
Dana classification	10.2.1.2
Crystal symmetry	Tetragonal ditetragonal dipyramidal H-M symbol: (4/m 2/m 2/m) Space group: P 4/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, firous to columnar, massive
Crystal system	Tetragonal
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

Bismoclite is a bismuth oxohalide mineral with formula BiOCl. The name was derived from its chemical constituents. It is a secondary bismuth mineral composed of bismuthyl ions (BiO⁺) and chloride anions. It is member of the matlockite group.

It was first described in 1935 from alluvium near bismuth-bearing pegmatites in South Africa. It has been found in association with granite pegmatite and in greisen. Associated minerals include: bismutite, mica, jarosite, alunite, cerussite, atacamite, connellite. Ocurrences 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.