PHYSIOGRAPHY. CLASS n. 



Streak white. Transparent... translucent, fre- 



quently even opake, particularly when impure. 

 Hardness = 7-0. Sp. Gr. = 2-690, of a snow- 



white crystallised variety. 



Compound Varieties. 1. Faces of composition 

 parallel, axis of revolution perpendicular to a face 

 of P 4- oo ; the individuals being continued be- 

 yond the face of composition. 2. Individuals 

 joined in a face of P oo ; this is as it were the 

 supplemental mode of composition to the pre- 

 ceding one. Frequently larger crystals are made 

 up of alternating laminae of two individuals, and 

 often faces of composition assume the appearance 

 of cleavage. 



Implanted globules, reniform, stalactitic shapes : 

 surface smooth, granulated, or drusy ; compo- 

 sition columnar, generally impalpable ; often a 

 second time composed into granular or curved 

 lamellar masses. Massive : composition granular 

 or columnar, and often impalpable, and then the 

 fracture becomes conchoidal and splintery. Some- 

 times a second composition produces indistinct 

 granular or thick lamellar masses. Certain very 

 thin columnar compositions, if cut en cabochon 

 parallel to the fibres, shew an opalescent light. 

 Pseudomorphic crystals, in the shape of hexahe- 

 drons and octahedrons, derived from octahedral 

 Fluor-haloide, of rhombohedrons and prisms de- 

 rived from rhombohedral Lime-haloide, of lenti- 

 cular forms from prismatoidal Gypsum-haloide. 



