230 PHYSIOG11APHY. CLASS II. 



Simple forms. P (P) ; Pr (s) ; ?r + 2 (0 ; 



?r+oo(o); Pr+oo (g). 

 Char, of Comb. Prismatic. 



Combinations. 1. P. Pr + oo. Pr -f x. Sim. 

 Fig. 10, without P. Oberstein, Deuxponts. 



2. Pr. P. Pr+x. ?r-f oo. Strontian, Scotland. 



3. ?r. P. Pr -f 2. Pr + <x. Pr -f oc. Fig. 22. 

 Andreasberg, Hartz. 



Cleavage, P, also Pr -f oc, and a little more dis- 

 tinctly Pr -f- oo, though imperfect in all direc- 

 tions. Fracture uneven, imperfect conchoidal. 

 Surface, f r and P streaked parallel to their com- 

 mon edges of combination ; so are also the faces 

 of several other forms appearing between Pr and 

 P ; Pr -j- 2 uneven ; Pr -f oo generally rough or 

 uneven ; Pr -f- <x> smooth, but in most cases di- 

 vided into four faces meeting at very obtuse 

 angles, as in certain hexahedral varieties of octa- 

 hedral Fluor-haloide. 



Lustre vitreous. Colour white prevalent, passing 

 into grey, yellow, red, and brown. Streak white. 

 Semi-transparent ... translucent. 



Brittle. Hardness = 4-5. Sp. Gr. 2 392, crys- 

 tals from Andreasberg. 



Compound Varieties. Twin-crystals. Face of 

 composition parallel, axis of revolution perpendicu- 

 lar to one of the faces of P + QD. The individuals 

 are continued beyond the face of composition, and 

 produce the common cruciform crystals, one of 

 which is represented in Fig. 40. Massive : com- 

 position granular, rare. 



