Abstract
Krupkaite, CuPbBi3S6, from the Juno Mine at Tennant Creek, Northern Territory, Australia, is orthorhombic, space group Pmc21 with a = 4.003(3), b = 11.200(9), c = 11.560(9) Å. Diffraction data were recorded with an equi-inclination diffractometer equipped with a proportional counter as detector. A least squares structural refinement, to an R value of 9.7 percent, permitted distinction between lead and bismuth on the basis of bond distances. The lead atom is coordinated to five sulfur atoms at distances from 2.89 to 3.02 Å; two additional sulfur neighbors are located at 3.27 Å. The Bi(l) atom has three sulfur neighbors at 2.65 Å and 2.79 Å and four more distant sulfur neighbors at 2.98 Å to 3.11 Å. The Bi(2) atom has three close sulfur neighbors at 2.54 Å and 2.19 Å and four more distant sulfur atoms at 2.99 Å to 3.38 Å. The Bi(3) atom has three neighbors at 2.64 Å and 2.63 Å, three more distant sulfur atoms at 3.00 Å to 3.10 Å and a seventh sulfur neighbor at 3.57 Å. The copper in the structure is mostly ordered (up to 80 percent) into one of the two sites available, to give the copper atoms a distorted tetrahedral coordination. In addition there is also an overall ordering of lead and bismuth atoms wich is determined by the semi-exclusion of copper from one of its sites in order to avoid a close interaction between copper and bismuth atoms. The major distortions in the structure away from the bismuthinite and aikinite arrangements are the result of this effect. The structure of krupkaite is based on the c ribbon, a structural element of bismuthinite derivatives previously suggested by Ohmasa and Nowacki (1970) and which has recently been found in the structure of gladite, PbCuBi5S9, by Kohatsu and Wuensch (1973). Its structure as such is in disagreement with the extensive series of super-structures based on aikinite that have been proposed to occur in the Bi2S3-CuPbBiS3, system by Welin (1966) and Moore (1967).
