4 ^ Defcripiion of the Arfeniates 



of the mineralogy of the countT of Cornwall, as far as It was 

 then known. Others fecm to have pofleflcd only imperfeft 

 fpecimens of arfeniale of copper, as none of the forms which 

 they attribute to its crj-ftals can belong to it, Befidcs, they 

 all confound with this ore thofe cubic cryftals, of a very 

 beautiful green colour, which are found in Muttrell mine, 

 contiguous to Huel Gorland mine ; and which, according to 

 the analyfis, made with the greateil care and ability, by 

 Mr. Chenevix, are of a nature totally diflerent, and cannot 

 properly be clafl'ed anions; copper ores, as they contain but a 

 very inconfiderable quantity of that metal. 



The exiftcnce of arfeniate of copper feems, however, even 

 at this day, to be an objeft of doubt among the French mi- 

 neralogifts; for the abbe Haiiy does not mention it in the 

 28th and following numbers of \ht Journal des Mhies, al- 

 though they contain an interefting extraft of a fyftem of 

 mineralogy, which he was then preparine for the prefs ; nor 

 has M. Fourcroy even hinted at it, in his Sjjiemc des Con- 

 voijfances Cb'tmiqueSy lately publiflied. 



It is now above twenty years (ince arfeniate of copper was 

 difcovered in the county of Cornwall ; it was firft found cither 

 in Carrach mine, in the parifh of Gwennap, or in Tincroft 

 mine, in the pariih of Allogan. Its matrix, like that of 

 almoft all the copper ores of this country, was fiiiceous, and 

 confided of a decompofed granife, of which the greateft part 

 of the feld-fpar had pafl'ed into the Hate known by the name 

 oi kaolin. It was accompanied with gray vitreous copper 

 ore, frequently in confiderable mafles; alfo with much black 

 oxide of copper; and with various oxides of iron. 



The arfeniate here fpoken of, which had never been found 

 in large quantity, had ceafed to exift in the above-mentioned 

 mines, when Hucl Gorland mine, lately wrought, began to 

 enrich hiineralogy with this uncommon fubdance. The ma- 

 trix of this is likewife fiiiceous; fometimes cryftalline; and 

 fometitnes in an amorphous mafs. Here and there we find 

 mixed with it, in greater or lefs profufion, all the known 

 oxides of copper ; many of the argillaceous oxides of iron; 

 alfo gray vitreous copper ore; yfenical pyrites; and the rich 

 deep-coloured yellow copper ore. This lall is often found 

 differing from its ufual appearance, in a manner which, I 

 believe, has not hitherto been taken notice of. I think it 

 Ihould make a diftinft variety among the deep yellow copper 

 ores, under the name oi yellow he?natttic copper ore. 



When the combination of copper with iron and fulphur 

 is rich in metal, (for, when it is poor, it is only a martial 

 pyrites mixed with a little copper,) its appropriate colour, 



wh«a 



