38 MEMOIR ON EMERY. 



the last, is strongly basic, containing a little more than thirty 

 per cent, of silica. 



CHLORITE. 



With the emery of Gumuch-dagh we find a chlorite. It 

 is in compact masses, composed of an agglomeration of small 

 crystalline plates, and contains octahedral crystals of magnetic 

 oxide of iron. Analysis gives as its composition : 



Silica 27.20 



Alumina ' 18.62 



Protoxide of iron 23.21 



Magnesia 17.64 



Water 10.61 



It is identical with the chlorite of Mont des sept-Lacs which, 

 gave M. Marignac 



Silica 27.14 



Alumina 19.19 



Protoxide of iron 24.76 



Magnesia 16.78 



Water .' 11.50 



It is the same as the chlorite of St. Christophe and the 

 ripidolite of Kauris and of St. Gothard. The formula given 

 by von Kobell is 2Mg Al+3(Mg Fe) 2 Si + 6H. 



MAGNETIC OXIDE OF IRON. 



This is found with the emery of every locality. It enters 

 into the composition of the emery itself, and is also found on 

 the surface in regular octahedral crystals. We find it fre- 

 quently massive and of strong polarity. That of Gumuch- 

 dagh contains a trace of titanic acid. 



OLIGIST IRON. 



It is associated with all the emeries, and sometimes enters 

 into their composition. It is also found in detached masses. 

 either amorphous or as crystallized specular iron. 



HYDRATED OXIDE OF IRON. 



This oxide of iron is not unfrequently found with emery, 

 covering the surface. It is found with pyrites having resulted 

 from the decomposition of this mineral. 



