392 Harrington — Composition of Canadian Amphiboles. 



Art. XXXYIII. — On the Composition of some Canadian 

 Am pinholes ; by B. J. Harrington. 



The writer is indebted to the Rev. W. P. Borhart, B.A., 

 for specimens of a beautiful variety of amphiboles from the 

 township of Grenville in the Province of Quebec. It had 

 been mistaken for garnet notwithstanding its characteristic 

 amphibole cleavage and optical characters. The specimens 

 received are all massive and most of them show, in addition to 

 eminent prismatic cleavage, a jointed structure, the jointage 

 planes making various angles with the cleavage planes. The 

 color is reddish-brown and the mineral shows a degree of 

 transparency not commonly found in the species. Flakes 

 obtained by cleavage exhibit an extinction angle of 16°. The 

 specific gravity was found to be 3-110 at 15° C. and the hard- 

 ness 6 or a little over. In composition the mineral is interest- 

 ing on account of the large proportion of fluorine which it 

 contains. The presence of this element has been observed in 

 many amphiboles but as a rule in much smaller quantity. The 

 quantitative analysis of a specimen of the mineral gave the 

 following results : — 



Silica 45*50 



Titanium dioxide 068 



Alumina 12*25 



Ferric oxide 0*28 



Ferrous oxide 0*75 



Manganous oxide O'll 



Lime ..... 13'31 



Magnesia 20-63 



Soda 2-76 



Potash _. 1-76 



Water _ 0'40 



Fluorine : 2-80 



101-23 

 Oxygen equivalent to fluorine 1*17 



100-06 



Another specimen gave 2*93 per cent of fluorine, a larger 

 proportion of this element than has been observed in any other 

 amphibole, so far as the writer is aware. It was estimated by 

 Rose's method, and on converting the calcium fluoride into 

 sulphate the amount obtained in each case agreed almost 

 exactly with the theoretical. The water was estimated 

 directly by fusing in a platinum boat with the mixed car- 

 bonates of sodium and potassium in a current of dry air and 

 collecting in a chloride of calcium tube. In the dry atmosphere 



