Original paper

The crystal structure of gustavite, PbAgBi3S6 Analysis of twinning and polytypism using the OD approach

Makovicky, Emil; Topa, Dan


The crystal structure of gustavite Pb1.06Ag0.95 Bi2.80Sb0.20S5.99 from Rotgülden, Lungau, Salzburg Land, Austria, was refined to R1 = 2.76 % using single-crystal X-ray diffraction data. Refined unit-cell parameters are a 7.0567(14), b 19.6905(39), c 8.2219(16) Å, β 106.961(3)°, unit-cell volume 1092.7(2) Å3and space group is P21/c. The structure contains a bicapped trigonal prismatic Pb site, a [001] string of Ag and Bi1 octahedral sites and a similar string of Bi2 and Bi3 coordination octahedra. Sb is concentrated in the Bi3 site whereas Bi1 and Ag contain a fraction (0.1-0.14 atom) of the opposite species; the latter is explained by a presence of twin lamellae or antiphase domains in the crystal. In accordance with its frequently observed twinning, gustavite is an OD (order-disorder) structure that can be described by zig-zag unit layers with layer symmetry P(2/n) 21/c 2/m and the interlayer symmetry elements {(22/n1,1/2) 21/n1/2,221/2/a2}. An alternative OD description uses planar unit layers with the layer symmetry P(2/b)21/c2/m and the interlayer elements 22/n1,-1/221/n1/2,2 21/2/a2. The former description adheres closely to the details of coordination of bismuth observed in the structure whereas the latter description is based on a more abstract structure model.


gustavitepb-ag-bi sulfosaltcrystal structuretwinningpolytypismod character