44 PHYSIOGRAPHY. 



Mica. 



iv. Trappean Aster-Mica. BREITHAUPT. 



Primary form. Acute rhomboid. 



Cleavage as above. 



Lustre peariy. Color black to dark brown. Optical axis as 

 above. Streak yellowish grey. 



Flexible in thin lamina. Hardness (scale of BREITHAUPT) = 

 2-50. ..30. Sp. gr.== 2.776. 



v. Axotomous Aster-Mica. BREITHAUPT. 



Primary form. Acute rhomboid. P on P = 67, about. 



Lustre pearly. Color greenish grey, to white. Optical axis 

 single. Streak white. 



In thin laminae, flexible. Hardness (scale oi'BREiTHAUPT) = 

 250. Sp. gr. = 2-780. 

 1. This is the variety from Munroe, (N. Y.) 



vi. Dichromatic Aster-Mica. BREITHAUPT. 

 Primary form. Acute rhomboid. Inclination of P to the axis = 

 15 14' to 15 15'. 

 Cleavage as above. 



Lustre pearly. Color green. Green parallel with the vertical 

 axis, hyacinth red at right angles to it. 



Flexible in thin laminae. Hardness (scale of BREITHAUPT) = 

 275. 

 1. From Zillerthal and from Binden in Switzerland. 



vii. Black Aster-Mica. BREITHAUPT. 

 Color black. Olive-green, in very thin laminae. 

 Sp. gr.== 2-507. 



viii. Lepidolite Rock-Mica. BREITHAUPT. 



Primary form. Oblique rhombic prism. MonM = 119. 

 Cleavage parallel with M perfect, with the shorter diagonal 

 only in traces. 



Lustre pearly. Color pale red, to light grey. Optical axis double. 

 Streak white. 



Flexible in thin laminae. Hardness (scale of BREITHAUPT) = 

 3-0. Sp. gr. = 2-827 . . . 2-855. 



1. To this species, belongs the varieties of Mica, called Lepidolite, and 

 some others. 



