Pirquitasite, Ag2ZnSnS4

Pirquitasite, ideally Ag2ZnSnS4 (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 (Ag1.87Cu0.13)(Zn0.61Fe0.36Cd0.03)SnS4. One Ag atom is located on Wyckoff site Wyckoff 2a (symmetry (4) over bar..), the other Ag atom is statistically disordered with minor amounts of Cu and is located on 2c ((4) over bar..), The (Zn, Fe, Cd) site on 2d ((4) over bar..), Sn on 2b ((4) over bar..), 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 is I (4) over bar, rather than I (4) over bar 2m as previously suggested. The structure was refined under consideration of twinning by inversion [twin ratio of the components 0.91 (6): 0.09 (6)].