PHYSIOGRAPHY. 



Pyroxene. 



135 



ture conchoidal, sometimes perfect . . . uneven. Surface, 

 r striated vertically, P sometimes rough. 



Lustre vitreous, inclining to resinous. Color green, often 

 inclining to brown, and passing into grey and white, and 

 also into black. Streak white . . . grey, corresponding to 

 the color. Transparent to opake. 



Brittle. Hardness =5-0 ... 6-0. Sp. gr. =3-349, an 

 ash-grey variety. 



Compound Varieties., Twin-crystals : face of compo- 

 sition parallel, axis of revolution perpendicular to r. 



Fig. 358. 



Sometimes crystals of this kind are in cruciform aggrega- 

 tions. Massive varieties, compound in the direction of P, 

 as in Sahlite ; this must not be taken for cleavage, as it 

 does not continue throughout the whole mass, but only pro- 

 duces more or less thick -laminae, often separated from each 

 other by some extraneous substance : it often possesses a 

 slight pearly lustre : there is also composition parallel r, as 

 in Mussite. Massive : composition granular, of various 

 sizes of individuals, often but slightly cohering, but often 

 also, very intimately connected ; faces of composition rough. 

 The individuals of lamellar and columnar varieties, are in 



