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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, however, the existence of the diatomic bismuthyl ion is doubtful. (2001). 9780123526519, Academic Press. ISBN 9780123526519
It is a 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. 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.
Crystal structure
The crystal structure of bismoclite was found to be composed of linked , specifically a square antiprism. 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. 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.
Practical significance
Bismoclite is a rare secondary mineral, a product of the oxidation of basic bismuth ores in the presence of active chlorine ions. In addition, bismoclite does not represent the final oxidation product. For example, during the oxidation of native bismuth under hypergenesis conditions, the intermediate product is bismuth chloride, and the final product is a sparingly Bismutite. Rundqvist D. V., Tatarinov P. M. Minerals and parageneses of minerals from endogenous deposits. — Leningrad: Science, Leningrad branch, 1975. — 131 p. For this reason, bismoclite is found in deposits of bismuthinite and native bismuth in much smaller volumes than the similar minerals bismite and bismuthinite, in which it is often present as an impurity. With the same success as these latter, it can be used to obtain bismuth and its compounds. However, the main significance of bismoclite is purely scientific, allowing more accurate monitoring and determination of geochemical processes in zones of oxidation and weathering of the main bismuth ores.
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