Bergslagite, a mineral with tetrahedral berylloarsenate sheet anions

Abstract

The mineral bergslagite, ideal formula CaBeAs0 4 (0H), occurs in association with schefferite, tilasite, manganberzeliite, svabite, barite and calcite as veinlets in hematite ore from Lângban, Sweden. Its structure has been determined from single crystal X-ray intensities by direct methods. Unit cell parameters: a = 4.8818(9), ¿> = 7.809(1), c= 10.127(1) A, 0 = 90.16(1)°; Ζ = 4. The structure was refined with similar results in space groups Ρ1 and P2JC.With P2Jc symmetry, values of R = 6A% and R w = 7.2% were obtained. This mineral is isotypic with datolite, herderite etc. and the structure consists of tetrahedral sheet anions and Ca 2 + layers stacked along a. Be and As atoms alternate at the nodes of the 4 and 8 ring tetrahedral net, except for a minor substitution of As 5+ by Si 4+ and probably Be 2 + . The distances r-O(nbr) are shorter than T-O(br) for both As0 4 andBe0 3 (0H) tetrahedra, but the As centred tetrahedra are more regular. Each Ca0 6 (0H) 2 polyhedron (distorted square antiprism) shares an edge with three more polyhedra to form a polyhedral layer in the be plane. Berylloarsenates structurally related to silicates seem to be rare, in contrast to beryllophosphates.

Alpine Minerals: A review of the Most Famous Localities of the Central Swiss Alps

“…Bergslagite from Falotta had been studied before it was described as a new mineral (Hansen et al 1984), but unfortu- Table 9. Minerals from Falotta (abandoned Mn mine).…”