38 PHYSIOGRAPHY. 



Mica. 



1. It is fusible before the blow-pipe, yielding moisture ; with soda, it 

 melts into a white globule ; with salt of phosphorus, flocculi of silica ap- 

 pear. It appears, therefore, to be some earthy silicate. 



MICA. Rhombohedral Talc-Mica. MOHS. 



Primary form. Oblique rhombic prism. M on M' = 

 120. M on P = 98 40'. 



Secondary forms. 



Fig. 297, 



Fig. 298. 



Acworth, (N.H.) Greenfield, (N.Y.) 



Fig. 297. P on & = 90. M on &=120. P on M= 

 98 40'. P on M'=81 20'. Fig. 298. P on o = 90. 



Cleavage, parallel with P highly perfect, and easily ob- 

 tained ; also traces of cleavage parallel with M M'. Frac- 

 ture scarcely observable, uneven. Surface, k and M, hor- 

 izontally streaked ; the other faces, particularly P, smooth. 



Lustre pearly, often inclining to metallic upon P: the 

 other faces, if they are smooth enough, present a kind of 

 lustre between vitreous and adamantine. Color various 

 shades of grey, generally passing into green, brown, and 

 black; also with white and red, (particularly, peach- 

 blossom red.) Superficial tinges of pinch-beck brown. 

 Streak white, grey. Transparent, imperfectly . . . translu- 

 cent on the edges. It is less transparent in the direction of 

 the axis, than perpendicular to it ; and generally exhibits 



