Granular Sulphuret of Copper

Among my Cornish specimens of Gray Copper, I have long retained one, peculiar for several acute bipyramidal dodecaëdrons of a dull slightly metallic lustre, rough surface, and grayish brown colour, that are dispersed about it. The greater part of the specimen is Quartz and Common Copper Pyrites, the surface of which is covered with many rhomboidal dodecaëdrons of Gray Copper, partly imbedded in each other: the pyramidal dodecaëdrons are scattered among these, but not imbedded. Their fractured surface is dull, and exhibits a fine granular texture and grayish yellow colour: their hardness is less than that of Common Copper Pyrites, and they are rather sectile. It appears to me probable that they may be the same variety of Copper, Pyrites, only crystallized; as that commonly called Blistered Copper, which the Count de Bournon has lately distinguished by the name of Cuivre et Fér sulfuré d’un jaune pale et d’un grain fin et compacte; of which tab. 432 is a representation.

The middle figure shows the apparent proportion of the crystals magnified; they are seldom so short as Quartz, hut appear occasionally to be longer than this figure. The right hand figure shows a truncated one, with blunt terminal edges; and the left hand figure is intended to show the fracture, which is rather rugged, and shows the yellow metallic lustre, proper to it according to the Count de Bournon.