PHYSIOGRAPHY. 



Gypsum. 



241 



Fig. 222. 



Bex, Switzerland. 



Fig. 218. Primary form, having the longer and shorter ter- 

 minal edges replaced. P on I =108 3' 19". P on/= 

 124 4V 43". /on/=110 36' 34". / on Z=143 53' 

 22". (trapczienne. HAUY.) Fig. 219. The same, altered 

 only through the additional planes k. P on k = 134 2 1 7 

 40". k on Z = 153 41' <69". (progressive. HAUY.) 

 Fig. 220. The same as Fig. 218, with the addition of 

 planes n through the replacement of the acute terminal an- 

 gles, (equivalente. HAUY.) Fig. 221. The same with 

 Fig. 220. excepting the substitution of planes o for f. o on 

 o =71 40' 32". (quaterno bisunitaire. HAUY.) Fig. 

 222. Lik'e Fig. 218. with the addition of planes r, and the 

 truncation of the acute, lateral edges, (disjoint &. HAUY.) 



Cleavage, parallel with P highly perfect, and easily ob- 

 tained ; with M and T imperfect, the former of these being 

 of a conchoidal appearance, while the former is obtained 

 with difficulty, on account of the flexibility of the mineral in 

 that direction, and often presents a fibrous aspect. Frac- 

 ture scarcely perceptible. 



Surface. P and I streaked, parallel to their common 

 intersections. The faces e and / often rounded, which 

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