Rietveld crystal structure refinement of tennantite, Cu-6(Cu0.48Fe5.52)As4S13

The crystal structure of Cu-6 (Cu0.48Fe0.52) As4S13, a badcrystallized natu ral tennantite sulphosalt found in Villahermosa del Rio (Castellon, Spain), has been refined by the Rietveld method using X-ray powder diffraction. Th e lattice parameter is a = 10.2157(2) Angstrom and the space group is I (4) over bar 3m. The used starting structural model was the isomorphous sulpho salt tetrahedrite. The Rietveld refinement converged to final crystal struc ture and profile indicators: wRp = 0.0544, Rp = 0.0426, R-Bragg 0.1266 and R(F) = 0.1739. The structure consists on a homogeneous frameworks built up from tetrahedra with common vertices. The full occupation of Cu2+ in tetrah edral sites and the incorporation of Fe3+ substituting Cu3+ in triangular s ites were explicitly established by Rietveld method. No silver content was found in this sulphosalt by electron microprobe analysis. The characteristi c tetrahedral habit is considered according to the Donnay-Harker law. A fas t review about crystal structure determination from powder data is included .