The crystal structure of neyite, Ag2Cu6Pb25Bi26S68

The crystal structure of type neyite from Alice Arm, British Columbia, was determined from single-crystal X-ray diffraction data with the agreement factors R-1 = 0.037 (0.072 for all) and omegaR(2) = 0.078. The structural formula supported by the new electronmicroprobe data is AgCu(3)Pb12.5Bi(13)S(34) (Z = 4); the lattice parameters are a 37.527(6), b 4.0705(6), c 43.701(7) Angstrom, beta 108.801(2)degrees, space group C2/m, The structure contains 26 independent large-cation polyhedra, one Ag site and three Cu sites. It can be described as an alternation of triple-octahedron (111)(PbS)-like layers with (100)(PbS)-like layers two atomic planes thick. Both sets of layers are (a) sheared, giving rise to tetrahedral Cu sites, and (b) truncated by wavy PbS-like layers (001)(ney), three atomic planes thick. The resulting structure can be described as a box-work of (100)(Pbs)-like layers enclosing (111)(PbS)-like fragments. Several hypothetical structures based on the neyite principle have been derived.