CRYSTAL STRUCTURE OF OWYHEEITE, AG1.5PB4.43SB 6.07S14: REFINEMENT FROM POWDER SYNCHROTRON X-RAY DIFFRACTION

Abstract

The crystal structure of owyheeite, a natural Ag-Pb-Sb sulphosalt from hydrothermal veins at Kutná Hora in central Bohemia, Czech Republic has been refined from powder X-ray synchrotron data, with a final Rwp = 4.1 %. The symmetry is monoclinic, space group P21/c, with a = 4.1035(1), b = 27.3144(3), c = 22.9366(3) Å, β = 90.359(1)°. The structural formula is Ag1.5Pb4.43Sb6.07S 14, with Z = 4. The structure of owyheeite contains 26 independent atoms: four Pb sites, one mixed Pb/Sb site, five Sb sites, one Ag site, one mixed Ag/Sb site and 14 S sites. All of them are in general Wyckoff position 4e of the space group P21/c; no special positions are occupied. The powder synchrotron diffraction pattern showed weak diffraction reflections indicative of a 2a superstructure. Three types of aggregates of coordination polyhedra can be recognized: three-fold columns of bicapped trigonal coordination prisms of Pb, two-strand ribbons of Sb and four-strand ribbons of 2 Sb atoms and 2 mixed sites Sb/Ag and Pb/Sb. A typical feature of the owyheeite structure is an ordering of Sb atoms to form lone electron pair micelles. Electron probe microanalysis gives (mean of 10 point analyses in wt. %): Ag 6.51(12), Cu 0.18(2), Pb 45.03(24), Sb 28.69(33), S 19.66(19), Total 100.08. Owyheeite belongs to a broad family of rod-based sulphosalt structures with the chess-board arrangement of the rods. © 2007 E. Schweizerbart'sche Verlagsbuchhandlung.