Arsenico-ferriferous, or Grey Sulphuret of Copper. Fahl-ore

Grey Copper has been found in several Mines in Cornwall. I have a neat little specimen in Tetraedrons from Tavistock, in Devonshire, by favour of John Taylor, Esq.

The present very neat specimen came from North Wales, and has many characters in common with the vitreous Copper Ores found in Cornwall: it is, however, more brittle and differs in its crystallization. This Ore varies in its contents, the specimens from Cornwall having only Copper, Iron, and Sulphur; while the foreign ones sometimes contain Silver, Arsenic, and Antimony. Its neat and smooth grey steel-like appearance makes it tolerably distinct. It is more shining than the usual vitreous Ore in the fracture, which is mostly small, conchoidal, and bluntish.

The present specimen has but little variation in external colour, and, though easily scraped with a knife, is rather harder than the common vitreous Copper.

The right hand lower figure shows the regular tetrahëdron, or primitive crystal, and that on the left hand shows some of its modifications, which are sometimes rather irregular. A fragment of this specimen heated by the blowpipe was found to be difficult of fusion : it gave out arsenical vapours, and was reduced to malleable Copper without showing any signs of Lead. Spec. Grav. 4.4460–4.4560.

A specimen from Freyberg, according to Klaproth, was found to contain:

This analysis corresponds with the effect the blowpipe has upon the Welsh specimen.