Crystal structures and crystal chemistry of members of the cuprobismutite homologous series of sulfosalts

The crystal structures of cuprobismutite Cu (sub 8.05) (Bi (sub 12.83) Ag (sub 0.96) Pb (sub 0.15) Cd (sub 0.08) )S (sub 23.93) from Felbertal, Austria, with a 17.590, b 3.922, c 15.177 Aa, beta 100.71 degrees , space group C2/m, Z = 1, and of two samples of hodrushite (1) (Cu (sub 7.48) Fe (sub 0.45) )(Bi (sub 11.54) As (sub 0.40) Pb (sub 0.08) )S (sub 22.05) also from Felbertal, with a 17.562, b 3.920, c 27.150 Aa, beta 92.561 degrees , space group C2/m, Z = 2, and (2) (Cu (sub 8.08) Fe (sub 0.28) )(Bi (sub 11.51) Ag (sub 0.05) Pb (sub 0.08) Sb (sub 0.03) Cd (sub 0.08) )S (sub 21.91) fromSwartberg, South Africa, with a 17.535, b 3.900, c 27.109 Aa, beta 92.333 degrees , space group C2/m, Z = 2, were refined. All homologues consist of PbS-like accretional slabs of two distinct thicknesses interleaved with slabs containing paired coordination pyramids of Bi with Cu tetrahedra. Bi occurs in four different types of coordination polyhedra, from regular octahedra to capped prismatic polyhedra; Cu occurs in trigonal planar and tetrahedral coordination. Ag (and possibly Pb) substitutes for Bi in the central octahedron of cuprobismutite-like slabs, whereas Fe substitutes for Cu along slab boundaries.