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XXXV. On the Cri/stallific Fonns of the Natural and Arti- 

 Jicial Sulphuret of Bismuth. By William Phillips, F.L.S. 



F.G.S.8)C* 

 A SPECIMEN was lately received from Cornwall by my 

 -^*- friend J. T. Cooper, Esq. for analysis ; and having ascer- 

 tained it to be sulphuret of bismuth, he was induced, by the 

 rareness of this substance in well-defined prisms, to permit me to 

 take several of them, in the hope of my being able to acquire 

 some information respecting their form by means of the reflec- 

 tive goniometer, and of any cleavages they might afford. I 

 also received from the above-named gentleman some of the 

 same substance artificially melted and crystallized. The spe- 

 cimen from Cornwall I recognized as having been brought 

 from Fowey Consols and Lanescot mines, (which are situated 

 about five miles to the east of St. Austel,) from having here- 

 tofore seen a specimen of the same kind at those mines, but of 

 which the crystals were extremely minute and imperfect. 



The prisms have the ordinary character of sulphuret of bis- 

 muth, in melting immediately when placed in the flame of a 

 candle, and they are bright externally and extremely flexible ; 

 accompanying them there are other prisms of the same general 

 form, which are dull and rough externally, and brittle ; and 

 the surfaces produced by fracturing them in any direction do 

 not evince any regular structure, but on the contrary are gra- 

 nular, and the particles of which they seem to be composed 

 are whiter than sulphuret of bismuth, and occasionally exhibit 

 a tinge of red. These prisms melt partially when placed in the 

 flame of a candle, throwing off", while melting, numerous bril- 

 liant scintillations, and may therefore perhaps be considered 

 as sulphuret of bismuth, including a mechanical admixture of 

 some other substance : and it is probably owing to this im- 

 purity that Mr. Cooper has not yet been able to complete 

 his analysis; the small quantity received from Cornwall not 

 having sufficed to enable him to detect its nature. 



The artificially crystallized sulphuret of bismuth afforded 

 only crystals so very slender as scarcely to exceed a human 

 hair in thickness, but extremely bright. I found them to con- 

 sist of rhombic prisms of 91'^ and 89"^, which one of them af- 

 forded alternately around the crystal. Their form is given by 

 the first and simplest of the succeeding figures, which shows 

 them to be modified by the })lanes h and /j the incidence of 

 M on M' being 91'^ 00', and of M on k \M° 30'. It is obvious 

 I'roni the mass inclosing these crystals, that they have at least 

 * ('tiinnninit;iiC(l In- the Author. 



one 



