Black Oxide of Copper

This has often a sooty appearance, but the shining semi-metallic surface produced by rubbmg is a particular character of it. It often has the appearance of having been sublimed by some process within the rifts of the rocks, and covers the Quartz, &c, which accompanies other copper ores. In many specimens it is evidently the result of the decomposition of other ores, sometimes forming into small concentric; seemingly botryoidal appearances, something like Iron Hæmatites. It is either pulverulent or in soft, smooth, friable crusts varying but little in colour from blueish to a dusky black, according to the quantity of Iron mixed with it. It appears scarcely to have been noticed as British till lately the Count de Bournon has made it public in his Catalogue, from whose observations it appears that most of the other ores of Copper produce it by decomposition.

It is also found in Hungary, Silesia, France, and Siberia. The Count de Bournon has kindly allowed me to select three Cornish specimens from his collection for figuring. One accompanied by Arseniate of Copper is coating Quartz crystals; another is the last stage of decomposition of blistered Copper Pyrites. I have recently received a specimen or two from a mine in Cornwall, in which the mammillated variety of the black Oxide is covered by spiculæ of dark green Arseniate of Copper; here the Arsenic Acid seems to have entered into combination with the Oxide of Copper, but in the smaller specimen figured the Arseniate seems to be decomposing, leaving the Copper on its surface.