1870.] Rev. Samuel Haughton on the Granites of Scotland. 315 



IV. White Mica. 



44-40 

 0-16 

 37*36 

 2-04 

 0-78 

 0-57 

 0-93 

 9-87 



0- 24 



1- 84 



98-19 



The specimen of Mica here analyzed came from veins in the Granite 

 quarry of Rubislaw, near Aberdeen, and occurs in large plates, associated 

 with red Orthoclase. It was carefully examined for lithia, but no trace 

 of this alkali could be found in it. 



The angles of the rhombic plates were 60 c and 1 20° exactly, and the 

 angle between its optic axes was found to be 72° 30'. 



The black Mica in large crystals is very rare, but it seems abundantly 

 disseminated in minute scales through most of the Scotch Granites. The 

 following analysis was made on specimens found :pear Aberdeen by Prof. 

 Nicol, and kindly forwarded to me by him, for the purposes of this 

 paper : — 



V. Black Mica. 



Silica 36-50 



Alumina 16*50 



Peroxide of iron 18*49 



Lime , I'll 



Magnesia 7*44 



Soda 0*92 



Potash 8*77 



Protoxide of iron 6*76 



Protoxide of manganese 1*80 



Water 1*60 



99*89 



This mica was carefully examined for fluorine, and found not to con- 

 tain any. 



Silica 



Fluosilicon (Si F 3 ) 



Alumina 



Peroxide of iron 



Lime 



Magnesia 



Soda 



Potash 



Protoxide of manganese 

 Water 



