[HARRINGTON] COMPOSITION OF SOME MONTREAL MINERALS 27 



Lepidomelane. 



Like the last mineral described this was obtained from one of the 

 coarse segregations of the nepheline-syenite at the Corporation Quarry. 

 The material examined occurred in rude crystals or plates measuring in 

 some cases as much as a quarter of 'an inch across. The colour was 

 black (green by transmitted light), and tSie lustre vitreous to adaman- 

 tine, optic axial angle small. The scales "showed very little flexibility. 

 The hardness was 3, and the specific gravity 3-269. The percentage 

 composition was found to be as follows: — 



Silica 32.96 



Titanium Dioxide 2 80 



Alumina 10.34 



Ferric Oxide 8.85 



Ferrous Oxide 27.19 



Man g.inous Oxide 2 . 79 



' Lime 64 



Magnesia . 73 



Soda 0.98 



Potash . 7.75 



Lithia 0.03 



Fluorine none. 



Water 4 36 



99.42 



Before the blo^\iDipe the mica fused to a black magnetic slag. It 

 was readily decomposed by hydrochloric acid, the silica being left in the 

 form of scales. 



If the titanium dioxide be calculated in with^ the silica the mole- 

 cular ratios are as follows : 



(E,0) (BO) : (R.O,) : (SiO,) 

 H40 444 156 607 



784 156 607 



5 14 



The composition is, on the whole, similar to that of the black mica 

 occurring in the nepheline-syenite of Monmouth, Ontario. In both 

 cases the specific gravity and the proportion of ferrous oxide are unusu- 

 ally high. 



