Pirquitasite, Ag2ZnSnS4

Abstract

Pirquitasite, ideally Ag2ZnSnS4(disilver zinc tin tetrasulfide), exhibits tetragonal symmetry and is a member of the stannite group that has the general formulaA2BCX4, withA= Ag, Cu;B= Zn, Cd, Fe, Cu, Hg;C= Sn, Ge, Sb, As; andX= 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 (Ag1.87Cu0.13)(Zn0.61Fe0.36Cd0.03)SnS4. One Ag atom is located on Wyckoff site Wyckoff 2a(symmetry -4..), the other Ag atom is statistically disordered with minor amounts of Cu and is located on 2c(-4..), the (Zn, Fe, Cd) site on 2d(-4..), Sn on 2b(-4..), and S on general site 8g. This is the first determination of the crystal structure of pirquitasite, and our data indicate that the space group of pirquitasite isI-4, rather thanI-42mas previously suggested. The structure was refined under consideration of twinning by inversion [twin ratio of the components 0.91 (6):0.09 (6)].