Bismoclite
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. 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 decahedrons, 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.