SULPHURET OF LEAD, COPPER, AND ANTIMONY. 331 



gravity is 5-033. It is not so easily cut as the preceding; 

 and the cut, though smooth, has not the sume lustre. Its 

 roost common colour has the redness of nickel, which is 

 deeper where cut ; but if this sulphurct be ever so little do- 

 composed, it acquires a blueish tint, and afterward assumes 

 the finest colours. 



3d, The double combination of copper and iron with Fahlette, 

 sulphur, but with a larger proportion of iron than the pre^. 

 ceding species. It is the fahlertz, or gray sulphuret of cop- 

 per and iron; the composition of which is copper 052, iron 

 0*33, and sulphur 0*14; and the specific gravity 4558. This 

 species is much harder than the preceding; but its hardness 

 varies according to the nature of the different substances 

 frequently interposed in it. It may be scratched, but 

 not cut; and the place scratched has neither the smoothness 

 nor the lustre of the two foregoing species. Its powder 

 varies from a full black to a black with a reddish cast, or a 

 reddish brown. The latter colour, as far as my observations 

 go, always indicates the presence of silver, which is com- 

 monly in the state of red autimouiated silver. It is much 



form its crystals most commonly assume. Sometimes the places of Chicfl}- cubical 

 its solid angles are occupied by equal sided triangular planes. Very 

 commonly these cubes have their faces slightly curvilinear. At 

 other times they are merely an aggregation, frequently irregular, 

 of other small cubes, which renders their figure very difficult to 

 discriminate. 



To the bunt kupferertz no doubt should be referred the cube, 

 which Werner, Estner, and several other German mineralogists, 

 give as one of the forms of the simple sulphuret of copper, to which 

 it appears to me incapable of. belonging. As to the octaedron, 

 given likewise by the same authors to the simple sulphuret of cop- 

 per, to which it is equally far from belonging, [ presume, that 

 some octaedra of red oxided copper, oxigenized to a maximum at 

 the surface, and turned black to a less or greater depth, may easily 

 have led to the mistake. Formerly there occurred in Cornwall a Variety, 

 variety of bunt kupferertz in thin laminae superimposed on one 

 another, and frequently of a fine blue colour at their surface. This 

 contained iron in smaller proportion than the bunt kupferertz, but 

 sufficient to render the sulphuret of copper incapable of being cut 

 with the knife, and when cut exhibiting the metallic lustre as the 

 simple sulphuret of copper. The fracture presents a coppery red 

 colour. 



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