100 PHYSIOGRAPHY. 



Char, of Comb. Prismatic. 



Combinations. 1 . Pr. Pr -f CD. Pr + QD. (Pot. sulf. 

 prismatique. HAUY.) 



2, P. (Pr+oo) 3 . (Pot.sulf.dodecaedre. HAUY.) 

 Sim. Fig. 7. without s* 



3. Pr. P. (Pr) 3 . P + oo. (Pr+oo) 3 . f r 4- CD. 

 Pr-f oo. Sim. Fig. 30., the edges between 

 d and s being replaced by the faces of P -j- oo. 



There is almost always regular composition paral- 

 lel to one or both faces of Pr. 



Cleavage, very indistinct, parallel to Pr and 

 pr 4- QD, the latter a little more apparent ; Traces 

 of Pr + QD. Fracture imperfect conchoidal ... 

 uneven. Surface; (Pr-f-co) 3 , and partly also 

 P -f x irregularly streaked parallel to their com- 

 mon edges of combination ; the rest of the faces 

 smooth. 



Lustre vitreous, inclining to resinous. Colour 

 white, yellowish or greyish, sometimes superfi- 

 cially greenish or blueish. Streak white, a little 

 shining. Transparent ... translucent. 



Rather brittle. Hardness = 2-5 ... 3-0. Sp, Gr. 

 =r 1-731. Taste saline and bitter, disagreeable. 



Its chemical formula is K S 2 , according to BERZELIUS, 

 corresponding to 



Sulphuric Acid 45-93. 

 Totash 54-07. 



. It occurs at Mount Vesuvius. The regular forms of 

 this salt have heen likewise ascertained to belong to the 

 prismatic system, by Dr BREWSTER, and by Messrs BROOKE 

 and LEVY. 



