PHYSIOGRAPHY. 



Prehnite. 



Cleavage, very distinct in the direction of P, less distinct 

 in that of M. Surface, P and al often streaked, the late- 

 ral faces streaked perpendicularly. 



Lustre vitreous, except upon P, which possesses pearly 

 lustre, particularly if produced by cleavage. Color, vari- 

 ous shades of green, as leek-green, mountain-green, apple- 

 green, siskin-green, &ic. ; passing into white and grey. 

 Streak white. Semi-transparent , . , translucent- 

 Brittle. Hardness =6-0 ... 7-0. Sp. gr. =2-926. 

 Compound Varieties. Reniform, globular, stalactitic 

 shapes : surface generally drusy ; composition columnar, 

 sometimes broad, imperfect and strongly coherent ; if the 

 particles of composition be distinct, the surface is often 

 pretty smooth. Massive : composition either columnar, as 

 above, or granular, and even sometimes impalpable. Some- 

 times compound varieties are again aggregated in a second 

 composition, the faces of composition being rough and un- 

 even. 



1. Before the blow-pipe, upon charcoal, it is transformed into a white 

 frothy scoria, which, on a continuance of the heat, melts into a compact, 

 colored globule. With borax, it melts into a transparent bead. In dilute 

 muriatic acid, it is slowly dissolved, leaving behind a flaky residue. 

 When heated, it exhibits electric poles. 



