Contribution to the crystallography of owyheeite

F. Laufek^1,2, R. Pažout³

¹Czech Geological Survey, Geologická 6, Praha 5, 152 00, Czech Republic

²Charles University, Faculty of Science, Albertov 6, Praha 2, 128 43, Czech Republic

³Institute of Chemical Technology, Technická 5, Praha 6,166 28, Czech Republic

laufek@cgu.cz

The mineral owyheeite belongs to complex sulphosalts of Ag, Pb and Sb whose structures present one of the most complicated problems in crystallography of inorganic compounds. Uncertainty existed about the crystallographic symmetry which was for a long time considered to be orthorombic [1] although a monoclinic symmetry with β near 90º was suggested. The crystal structure of owyheeite, structure formula Ag₂Pb₅Sb₅S₁₄, was refined from powder X-ray synchrotron data of a sample from hydrothermal veins at the Turkaňk Lode of the Kutná Hora Ag-Pb-Zn polymetallic deposit, Central Bohemia, Czech Republic. The data were collected on the Swiss-Norwegian diffractometer BM1B at the European Synchrotron Radiation Facility (ESRF, Grenoble, France, λ = 0.49953 Å, sample in a 0.3 mm glass capillary). The powder X-ray synchrotron diffraction pattern was indexed using the first 20 lines. The monoclinic symmetry was indicated by DICVOL04 [2] program with figures of merit M₂₀ = 37, F₂₀ = 267 (0.0014, 53). The synchrotron powder diffraction pattern was refined with the cell found by DICVOL04 using the "profile matching" option [3] of the program FullProf [4] in order to determine the space group. The systematic absences were consistent with the space group P2₁/c. The initial structural model was obtained by preliminary single crystal X-ray diffraction experiment (Makovicky, pers. com). The final structure was obtained through the Rietveld refinement in the program FullProf and refined to R factors R_wp = 0.041, R_B = 0.034 and χ² = 4.52.

Owyheeite, Ag₂Pb₅Sb₅S₁₄, space group P2₁/c, a = 4.1034(1), b = 27.3130(5), c = 22.9352(4) Å , β = 90.359(2)º, Z=4. The asymetric unit contains 26 atoms. The average structure exhibits fourteen S, one Ag, four Pb, five Sb sites and also two mixed sites, (Pb, Sb) and (Ag, Sb). The structure is presented in Fig. 1.

Fig. 1: Crystal structure of owyheeite

1. J. W. Anthony, Handbook of Mineralogy, Elements, Sulfides, Sulfosalts. Mineral Data Publishing,

USA, 1990.

2. A. Boultif, D. Louër, J. Appl. Cryst. 37, (2004), 724-731.

3. A. LeBail, H. Duroy, J. L. Fourquet, Mater. Res. Buletin., 23, (1988), 447-452.

4. J. Rodríguez-Carvajal, FullProf.2k, Laboratoire Léon Brillouin, France, 2006.