Lindstromite from Cobalt, Ontario

Abstract

The results of the characterization of a well-ordered lindströmite from the Drummond mine (also known as the Silver Miller mine), 3 km southeast of Cobalt, Ontario are reported. Chemical analyses by electron microprobe gave the composition Cu2.70Pb2.80Bi7.18Sb0.09S 15, intermediate between the ideal composition of lindströmite Cu3Pb3Bi7S15 and of krupkaite CuPbBi3S6. Least-squares refinement of the powder X-ray-diffraction pattern gave an orthorhombic cell, a = 55.99(3), b = 11.549(3), c = 4.010(1) Å, which is within error limits of the cell given for lindströmite from the type locality, Gladhammar, Sweden. The optical properties in reflected light and the indentation hardness are reported, and were found to be very similar to those of krupkaite and hammarite. It is not possible to distinguish among intermediate members of the bismuthinite - aikinite series on the basis of their optical properties or indentation hardness. Electron-diffraction patterns reveal a well-ordered 5a superlattice of the bismuthinite parent cell, the superlattice reflections are sharp, and there is no evidence of streaking along a*. High-resolution images show the perfectly ordered nature of the structure. The nature of compositional ordering processes in these bismuthinite - aikinite minerals is discussed.