PHYSIOGRAPHY. 



Manganite. 



Compound Varieties. Twin-crystals. 1. Face of com- 

 position parallel to Z, axis of revolution perpendicular to it. 



Fig. 290. 



A repetition of this law produces thick prisms, terminated 

 perpendicularly upon their axis by a rough face, which con- 

 sists of the apices of numerous individuals, or rather of nu- 

 merous particles of two individuals, alternating with each 

 other. 2. Axis of revolution perpendicular, face of com- 

 position parallel to a plane of the pyramid. 



Fig. 291. 



present a brown streak, being generally between 2-5 and S'O ; and some- 

 times in fibrous varieties, it is so inconsiderable as to soil the fingers and 

 write upon paper. On the contrary, their specific gravity is higher, and 



3* 



