The crystal structure of Cu1.6Pb1.6Bi6.4S12, a new 44.8 angstrom derivative of the bismuthinite-aikinite solid-solution series

The crystal structure of Cu1.60Pb1.62Bi6.38S11.97, idealized Cu1.6Pb1.6Bi6. 4S12, a new derivative of the aikinite-bismuthinite series from the metamor phosed scheelite deposit of Felbertal, Austria, with a 4.0074(9), b 44.81(1 ), c 11.513(3) Angstrom, space group Pmc2(1), Z = 4, has been solved by dir ect methods and difference Fourier syntheses to a residual R value of simil ar to 4.7%. The unit cell of this "four-fold derivative" contains two "bism uthinite-like" Bi2S3 ribbons and six "krupkaite-like" CuPbBi3S6 ribbons. Th e fully occupied Cu sites occur in zigzag [001] rows Delta y approximate to 0.25 apart; the third [001] row, in which the Cu sites are 71% occupied, i s Delta y approximate to 0.375 apart from them. The latter interval hosts a strongly zigzag pattern of 10% occupied Cu sites. Coordination polyhedra h ave been analyzed using the polyhedron-distortion parameters devised recent ly by Balic-Zunic & Makovicky. Cu1.6Pb1.6Bi6.4S12 occurs at Felbertal both as independent grains and as a component of exsolution pairs.