Subsulphuret of Copper, or Vitreous Copper Ore

This variety of vitreous Copper Ore is also found at Cooks-Kitchen, in Cornwall, but is very rare, I have received it among other favours from Mr. J. Taylor of Tavistock. It is worthy of remark, that the crystals are of a large size to what is usual, and the hexaëdral pyramids, which are placed base to base, are more or less elongated: thus has Nature sported with the crystallization, so as to prevent our measuring with certainty the angle of incidence at their mutual bases. Some of the crystals have the regular bevellings of Haüy, perhaps, not to be measured with certainty; and some of the crystals have many lateral faces, so as to give roundness, thus also to elude measure. The fracture is mostly irregularly glassy, or minutely conchoidal. This Ore is easily scraped or scratched with a knife to powder, but is not brittle. The colour is iron-grey within, darker on the outside: some specimens have the blue watch-spring lustre and iridescence. Spec. Grav., according to Kirwan, 4.129.

By analysis it is found to contain:

The matrix is a mixed sulphureted Oxide of Copper and Iron^* with Quartz, through which there runs a vein of the vitreous Copper Ore with the crystals.