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Crystal structure of owyheeite, Ag_1.5Pb_4.43Sb_6.07S₁₄: refinement from powder synchrotron X-ray diffraction

Frantiek Laufek¹, Richard Paout² and Emil Makovicky³

¹ Czech Geological Survey, Geologická 6, 152 00 Praha 5, Czech Republic
² Institute of Chemical Technology, Praha, Technická 5, 166 28, Praha 6, Czech Republic
³ Geological Institute, University of Copenhagen, Øster Volgade 10, 1350 Copenhagen, Denmark

^* Corresponding author, e-mail: laufek{at}cgu.cz

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 R_wp = 4.1 %. The symmetry is monoclinic, space group P2₁/c, with a = 4.1035(1), b = 27.3144(3), c = 22.9366(3) Å, ß = 90.359(1)°. The structural formula is Ag_1.5Pb_4.43Sb_6.07S₁₄, 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.

Key-words: owyheeite, crystal structure, Pb-Ag-Sb sulphosalt, Rietveld refinement, synchrotron powder data, Kutná Hora, Czech Republic.

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