Bindi, Luca2; Makovicky, Emil5; Nestola, Fabrizio3; De Battisti, Luca4
1 Geology, Department of Geosciences and Natural Resource Management, Faculty of Science, Københavns Universitet2 University of Firenze3 University of Padua4 FGL5 Geology, Department of Geosciences and Natural Resource Management, Faculty of Science, Københavns Universitet
description and re-investigation of the crystal structure
We have characterized the crystal structure of sinnerite, Cu6As4S9, a rare sulfosalt mineral from the ores of the Lengenbach quarry, Binn Valley, Canton Valais, Switzerland, by single-crystal X-ray diffraction and chemical analysis. We found sinnerite to be structurally identical to synthetic Cu6As4S9. It is triclinic, space group P1, with cell parameters: a 9.103(2), b 9.860(3), c 9.111(2) Å, α 90.27(2), β 109.53(2), γ 107.58(2)°, V 729.6(4) Å3, and Z = 2. Semi-quantitative SEM-EDS analyses confirmed the Cu6As4S9 stoichiometry. The crystal structure of an untwinned crystal has been refined to R1 = 5.45%. It consists of a sphalerite substructure with 2/5 of the tetrahedra replaced by AsS3 pyramids; four pyramids form As4S12 clusters around the vacant anion positions of the sphalerite archetype. These pyramids are linked into twisted and branched chain-like structures with compositions As3S7 and As5S11. The chains are linked by CuS4 tetrahedra. Packing of these chains results in the OD (order-disorder) character of the sinnerite structure.
Canadian Mineralogist, 2013, Vol 51, Issue 6, p. 851-860