The crystal structure of Ag-excess fizélyite from the Van Silver mine, just north of Squamish, British Columbia, Canada, was studied on the basis of X-ray-diffraction data collected from an untwinned single crystal. The structure was refined to R1 = 0.041 in space group P21/n, with unit-cell parameters a 19.2767(6), b 13.2345(4), c 8.7230(3) Å, β 90.401(2)°, and V 2225.3(1) Å3. The chemical composition of the sample, determined by electron-microprobe analysis, is Ag5.94Pb13.74Sb20.84S48, which reveals nearly one more Ag atom per formula unit than in the ideal composition, Ag5Pb14Sb21S48, presently proposed by the IMA for fizélyite. Except for an additional partially occupied Ag site (Ag2) and two split cation sites (Ag1 and M2) in our sample, fizélyite is isostructural with ramdohrite, CdAg5.5Pb 12Sb21.5S48. The structure of fizélyite contains chains of edge-sharing SbS6 octahedra connected by chains of alternating M1S6, (M1 = Pb + Sb) and SbS6 octahedra, forming slabs parallel to (100). The slabs of octahedra are linked by distorted AgS4 tetrahedra, M2S6 octahedra, and PbS8 polyhedra. The excess Ag in our fizélyite is mostly situated at the Ag2 site, and is likely responsible for the splitting of the Ag1 and M2 sites.
- Ag excess
- Crystal structure
- Single-crystal X-ray-diffraction
ASJC Scopus subject areas
- Geochemistry and Petrology