Crystal structure of harstigite, MnCa₆Be₄[SiO₄]₂[Si₂O₇]₂(OH)₂

Abstract

The structure of harstigite, MnCa6Be4[SiO4]2[Si2O7]2(OH)2 from Värmland, Sweden, is orthorhombic with space group Pnam, a = 9.793(2), b = 13.636(3), c = 13.830(3) Å, Z = 4 and Dx = 3.19 g cm−3. It was refined to R (unweighted) = 0.053 and R (weighted) = 0.050 using 3630 non-equivalent reflections. Harstigite is a mixed-anion silicate which contains [SiO4] tetrahedra (mean Si – O distance 1.637 Å), [Si2O7] groups (mean Si – O distance 1.623 Å), and in addition [Be(O,OH)4] tetrahedra (mean Be – (O,OH) distance 1.651 Å), [MnO6] polyhedra (mean Mn – O distance 2.222 Å) and [CaO8] polyhedra (mean Ca – O distance 2.507 Å). The ratio of single tetrahedra [SiO4] to double tetrahedra [Si2O7] in the structure is 1:1.