146 PHYSIOGBAPHY 



3. P - ^L-- 1 . *L fr + 1 



(f_ 2)* (Pr I) 5 



0) O O 



p r _ 2. Pr _ 1. | Pr. - ^L+2. 

 -I- -^^~ P ^*- (f+) 4 - 



Pr + QD. Fig. 171. 



Cleavage, P oo, highly perfect, and easily ob- 

 tained, traces of P + oo and Pr + oo. Frac- 

 ture conchoidal, scarcely observable. Surface, 

 R oo very smooth and even, some of the faces, 



particularly curved, or uneven. 



52 



Lustre resinous, inclining to adamantine, pearly 

 upon P QD. Colour yellowish- white, passing 

 into various pale grey, green, yellow, and brown 

 tints. Streak white. Transparent ... trans- 

 lucent. 



Rather sectile. Hardness = 2-5. Sp. Gr. = 6-266 

 of crystals resembling var. 1 . 



Compound Varieties. Twin-crystals very fre- 

 quent ; axis of revolution perpendicular, faces of 

 composition parallel to one of the faces of (P -f- oo) 5 . 

 In a similar composition, the variety Fig. 171., in 

 Mr ALLAN'S cabinet, has been observed. This 



