ORDER xiii. PRISMATIC SULPHUlt. 53 



101 59'; r (n) = 55 36' ; Pr = 46 15' ; 



Pr + OD (o). 



Char, of Comb. Prismatic. 

 Combinations. 1. P oo. P. 



2. P oo. |P 2. Pr. P. P+ oo. Fig.18. Sicily. 



3. P oo. | P 2. | P 2. Pr. Pr. P. 

 P -f oc. Artern, Thuringia. 



Cleavage, P and P -f oo, imperfect, difficultly ob- 

 tained, and interrupted. Fracture conchoidal, 

 sometimes highly perfect. Surface, Pr common- 

 ly rough, the rest of the faces generally smooth 

 and shining, possessing nearly the same physical 

 quality. 



Lustre resinous. Colour, several shades of sulphur- 

 yellow, inclining sometimes to red or green. 

 Streak sulphur-yellow, passing into white. Trans- 

 parent ... translucent on the edges. 



Sectile. Hardness = 15 . . . 2-5. Sp. Gr. =: 2-072, 

 crystals from Spain. 



Compound Varieties. Twin-crystals : axis of 

 revolution perpendicular, face of composition paral- 

 lel to a face of Pr.* Imbedded globules : surface 

 uneven ; composition impalpable, often impure. 

 Massive : composition granular, often impalpable, 

 strongly coherent ; fracture uneven, even, flat con- 

 choidal. Sometimes pulverulent. 



* This kind of regular composition has been observed by Dr 

 G. HOSE. H. 



