Peroxide or rather Hydrate of Copper
This specimen is remarkable, not only from its being unique, but from being found by Mr. Sheffield in Dalehead lead-mine, in Cumberland. The vitreous appearance might give occasion for dispute between the Neptunians and Volcanians; but as I consider both modes of formation to be more or less concerned in many instances where it has been imputed to one only, I shall leave it to every philosopher to consider it in his own way, as such a specimen may give equal force to either theory when considered alone.
This specimen consists of a green Oxide or rather Hydrate of Copper united to almost half its weight of Silex. It is quite vitreous or glassy in its fracture, with a semitransparency, full of irregular cracks or flaws, like the potter’s glaze, or like moderately diluted gum that is cracked after being left to dry, and when thinnest, not unlike cracked varnish. Its colour and brilliancy are quite similar to verdigrise, which is only a preparation from Copper; nor do we know many other substances which produce this beautiful green, which in some intances approaches the green Patina found on old coins. Under the blowpipe its brilliancy is lost, and it assumes a dark brown colour, but the fragment is difficult of fusion. Small pieces thrown into dilute Nitric Acid gradually lose the Copper they contain without effervescence, and the Silex remains unaltered in form. Of two grains and a half, about one grain and a fourth remained transparent when wet, but proved opaque white when dry, and possessed the characters of Silex.