The crystal structure of paderaite, a mineral of the cuprobismutite series

Abstract

Paderaite from Baita-Bihorului (Rezbanya, Rumanig) is monoclinic, a 28.44(8), D 3.90(3), c 17.55(8) A, 9 = 106.0(2), space group P2 /rn, Z = 2,Its crystal structure has been determined from data recorded with CuKa radiation on a single-crystal diffractometer. There are 20 metal and 22 sulfur atoms in two asymmetric units. Atom co-ordinations include octahedral @i), trigonal prismatic (Bi,Pb), trigonal to distorted tetrahedral (Cu), and quasilinear (Ag). Electron-probe microanalysis indicates a composition Cu5.eAg13Pb1.6Bifi.2A, This result is supported by the struc'ture anallnis, which yields typical atom co-ordinations and bonding for 12 Bi, I Pb, 6 Cu, and I Ag, The structure of padoaite is related to ttrose of Cu4Bi5Slo, cuprobismutite, and hodrushite. CJayers (so called after cuprobismutite) are present jn all four structures and determine their common 17.5-A cel dimsnsl6l. CJayers alternate with predominantly H-typ (i.e., sheared octahedral) layers (here designated D-layers after hodrushite) of different thickness, forming the group of compounds now termed the cuprobismutite series. Cu4Bi5S10 contains C-layers only, whereas cuprobismutite, paderaite and hodrushite feature both C- and D-layers.