Pirquitasite, Ag₂ZnSnS₄

Abstract

Pirquitasite, ideally Ag 2 ZnSnS 4 (disilver zinc tin tetrasulfide), exhibits tetragonal symmetry and is a member of the stannite group that has the general formula A 2 BCX 4 , with A = Ag, Cu; B = Zn, Cd, Fe, Cu, Hg; C = Sn, Ge, Sb, As; and X = S, Se. In this study, single-crystal X-ray diffraction data are used to determine the structure of pirquitasite from a twinned crystal from the type locality, the Pirquitas deposit, Jujuy Province, Argentina, with anisotropic displacement parameters for all atoms, and a measured composition of (Ag 1.87 Cu 0.13 )(Zn 0.61 Fe 0.36 Cd 0.03 )SnS 4 . One Ag atom is located on Wyckoff site Wyckoff 2 a (symmetry -4..), the other Ag atom is statistically disordered with minor amounts of Cu and is located on 2 c (-4..), the (Zn, Fe, Cd) site on 2 d (-4..), Sn on 2 b (-4..), and S on general site 8 g . This is the first determination of the crystal structure of pirquitasite, and our data indicate that the space group of pirquitasite is I -4, rather than I -42 m as previously suggested. The structure was refined under consideration of twinning by inversion [twin ratio of the components 0.91 (6):0.09 (6)].