Anatyjts of a new Variety of Lead Ore. %zi 



At other times, the cryftal having undergone the preceding modification, fo as to leave 

 a great part of the cubical faces, is fubje£l to another, which replaces each of the longi- 

 tudinal prifmatic edges by two planes, inclined upon the prifmatic faces, with which they 

 form an angle of i6i° 30', then a tetraedral pyramid, more or lefs truncated at the fum- 

 mit, feems placed on each of the longitudinal faces (the cryftals dill confidered as prifmatic) 

 the faces of which, taken two by two, are differently inclined ; two of them tend to meet 

 at the fummit in an angle of 143°, the two others in an angle of 116°. Such are the 

 different modifications of this ore, to which there is nothing fimilar among the fimple 

 carbonated leads. 



i\ll thefe varieties are extremely beautiful and perfeft in 'their cryftallization ; they are 

 generally of a light ftraw colour, though fometimes of a perfe<Slly colourlefs and clear 

 tranfparent white, with a luflre far more brilliant than the fimple carbonated leads. 



Its topographical hiftory I fliall tranfcribe in the words of Mr. GrevlUe. " About 

 " fourt^een or fifteen years ago, I purchafed a piece of this mineral at Matlock, in Derby- 

 *' (hire ; the ftiopkeeper not knowing from what mine it came, or unwilling to inform me, 

 " I left a commifTion for him to fend me all he could procure, and repeated my order for 

 " feveral years fucceflively : I traced fome fpecimens, which had been fold, and recovered 

 " them. The largeft cryftal. Dr. Darwin, of Derby, gave up to me. I fuppofed, from 

 " my enquiries, that it came from the diftridl of mines intended to be unwatered by the 

 " Cromford level, as I was afTured of my having no chance of any more till that level was 

 " compleated ; and fince that period the water has continued in a degree, that many 

 " mines which were then open, are now drowned." 



The cryftals are upon a large facetted galena, and commonly from half an inch to an 

 inch in length. The largeft mentioned in Mr. Greville's note, is an inch and a half long, 

 ah inch broad, and half an inch thick, of the fineft tranfparent yellow. This ore, 

 however, does not appear to be an exclufive produftion of this country; for there are 

 two fpecimens in Mr. Greville's colleclion, which are in much fmaller and peifedly white 

 cryftals, which feem perfeftly the fame ; but they are not of this country, and, as I believe, 

 come from the Hartz ; no doubt it will be found elfewhere, when the attention of natu- 

 ralifts ftiall have been more particularly directed to that objed. 



ANALYSIS. 

 One hundred parts,, chofen from a cryftal perfeflly franfparent, regular, and pure, were 

 reduced to powder ; during this operation they frequently caked, and offered an elaftic 

 refiftance, not unlike muriate of ammonia in the fame circumftances ; they were thrown 

 into a known weight of nitrous acid ; a fudden effervefcence took place, and the diminu- 

 tion was = 00,6, and the elaftic fluid was afterwards proved to he carbonic acid. As foon 

 as the efFervefcence had fubfided, there remained at bottom a white powder, infoluble 

 without the afhftance of heat; but after a flight ebullition, this refiduum was reduced to 

 00,1, which was fulphate of barytes, and quite foreign to the intimate nature of the 

 ore. Info the difTolution was poured cauftic ammonia, in preference to a fixed alkali, 

 4 becaufe 



