£5i* SLLPIJURET »F LEAD, COPPER, ISO ANTIMONY. 



ready mentioned, constitutes the only specimens T have yet 

 seen from any place except CornwaH. The groupe, which 

 assuredly is not English, was given to me as coming from 

 Siberia. Its gangue is an irregularly crystallized quartz, 

 part of which is of a dark blackish gray, in consequence of a 

 mixture of very minute particles of sulphuret of lead, im- 

 perceptible to the naked eye. The crystals of endellion are 

 covered by a slight stratum of green carbonate of copper ; 

 and some small crystals of common dudecaedral pyramidal 

 carbonate of lime (metastalique of Haiiy) are disseminated 

 among them as well as in the quartz. Several small parcels 

 of sulphuret of lead and blue copper are likewise observable 

 on it. 



Such is the result, which the most careful examination, 

 and continual attention to every thing, that could render me 

 better acquainted with this scarce and interesting substance, 

 enables me at present to lay before the Royal Society. I 

 am far however from imagining, that I have seen every thing 

 Fgohobfy dtber pertaining to its crystallization. Undoubtedly other varie- 

 ties, and other modifications, may exist ; and it is probable, 

 that, among the small number of specimens of it in different 

 collections, such may be found. From the numerous va- 

 rieties, that exist in a single groupe of this substance, its 

 primitive crystal appears to have a great tendency to be .mo- 

 dified : but the modifications of this crystal, which I have 

 given, are unquestionably sufficient, to render it easy to as- 

 certain any new ones, if they should occur. These re- 

 flexions are not introduced here without reason. Among 

 the different specimens of this substance examined by me, 

 1 have seen several crystals belonging to some of the varie- 

 ties I have given, on which there existed likewise slight 

 traces of planes belonging to other modifications, but which 

 - altogether impossible for me to determine. As an 

 •Vttmple of this I shall mention the crystal represented at PI. 

 VIII, fig. 27, not only because it is one of the most strik- 

 f'or elegance of form, but because it is iu my own pos- 

 on. The faces indicated by the letters x, y, and z, arecer- 

 ! owing to an intermediate retrogradation at the angles 

 oj the terminal faces: but the impossibility of measuring 

 uitn precision the angle of inclination between these planes 



