Compound Sulphuret of Bismuth, or Cupreio-plumbiferous Sulphuret of Bismuth

Mr. Patrin, in the year 1786, discovered the present Mineral in Catharineburg, in Siberia. It had been considered as Native Chromium by several eminent Mineralogists, until Mr. John published a memoir, proving that it was a Sulphuret of Bismuth, containing Lead and Copper in considerable quantities, as the analysis shows; its external characters, united with its composition, appear to me to mark it as a distinct species from the pure Sulphuret of Bismuth. The surface of the fresh fracture is very brilliant, of a colour generally resembling polished steel, but rather winter, sometimes it is rather redder, as if it then contained more Copper: it is soon tarnished, becoming at first yellow, then green, and at length blue and purple. The crystals are long prisms, much striated upon their surfaces, they are described by Karsten as six-sided, I have observed one or two decidedly so, but not regular hexaëdral prisms, the rounding of the faces and the striæ prevent any very nice decision, otherwise the supposition of the Count de Bournon, that the hexaëdral prism spoken of by Karsten is derived from an obtuse tetraëdral one, which the Count considers as the form of the needles of which the prisms appear generally to be composed, might happily be confirmed. The crystals that are closely enveloped in the Quartz, are dull grey upon the surface, but those that are exposed to the action of air or moisture, are covered with a dull green crust; which much exposed the crust becomes very thick and yellow externally: it consists of the metals in the stale of Oxyde. Before the blow-pipe it is easily melted; a great portion evaporates, and a globule of Lead, encrusted with Oxyde of Copper, remains. The crystals frequently contain grains of Gold; in the specimen I have figured some of the crystals are partially covered by a laminated substance like Galæna. Spec. Grav. 6.125.