248 Mr Haidiriger on Polyhalite. 



intersection of them with r about I9.'il\^. There were crystals 

 lining the cavities of some fissures in one of the specimens, but 

 so small that their form could be made out only by means of 

 a compound microscope. The massive varieties presented 

 striated faces of composition, as it is marked in the figure of 

 the crystals, the surface of which is also striated in the same 

 manner. They also show cleavage, but not very perfect, pa- 

 rallel to the faces, and these yielded 115^^ as an approximate 

 measurement. 



The colour is a very pale flesh-red, almost yellowish. 



The hardness, given in books as greater than that of calca- 

 reous spar, I found only 2.5 greater than rock-salt, but consi- 

 derably inferior to calcareous spar ; this is also the hardness of 

 the darker red fibrous varieties, which I examined for compa- 

 rison's sake. 



The taste of polyhalite, in every one of its varieties, is very 

 faint^ and has more of the bitter and astringent than of the sa- 

 line, which, when it is perceived, is owing to an admixture of 

 rock-salt. The solubility in water is also very inconsiderable. 



The specific gravity I found in one of the specimens, which 

 consists of pretty large individuals, = 2.782 ; in the other, 

 whose component individuals are more compressed between 

 their faces r and r, and which possesses more lustre upon the 

 faces of composition, I obtained 2.730 ; in another portion of 

 the same 2.746. The specific gravity of the red fibrous va- 

 riety was found = 2.770, very nearly the same as Stromeyer's 

 result, 2.7689. 



Whatever may be ascertained of the physical properties of 

 the two specimens mentioned above, and the variety of poly- 

 halite originally analyzed by Professor Stromeyer, tends to 

 unite them within one species. Even the traces of cleavage in- 

 clined to the direction of the fibres visible in the latter agree 

 with the position of the prism of 115°. A chemical analysis of 

 the more crystalline varieties would be now very interesting, 

 as it would no doubt perfectly establish the nature of this com- 

 pound, and likely also somewhat reduce the number of salts 

 found in the fibrous specimens. 



