248 



PHYSIOGRAPHF. 



Troostite. 



Secondary form. 



Fig. 452. 



P on a - 

 P on b - 

 a on b - 

 b on 6 - 



J 47 30' c. g. 

 122 00 



109 00 " 



120 00 " 



Irregular forms, grains. 



Cleavage parallel with b perfect, at right angles to the 

 axis less distinct, with P in traces. Surface, b smooth and 

 shining, P and a dull. Fracture conchoidal. 



Lustre vitreous, inclining to resinous. Color pale as- 

 paragus-green, yellow, grey, and reddish-brown ; none of 

 them bright. Transparent to translucent. 



Brittle. Hardness =5-5. Sp. gr. =4*0 . . . 4-1. 



Compound Varieties. Massive : composition granular. 



1. Heated before the blow-pipe, it becomes transparent and melts on 

 the edges. With borax, it dissolves giving the violet tinge of oxide of 

 manganese. It is dissolved with effervescence in muriatic acid, at the 

 same time giving out chlorine, and leaving a residue of silica. 

 2. Analysis. 

 By THOMSON. 

 Silica 30-650 



Protoxide of manganese 46215 



Peroxide of iron 15-450 



Loss by heat 7-300 



