ON PYROXENIC COMPONENTS IN CERTAIN VOLCANIC ROCKS. 81 



signs that they were beginning to be attacked. Peculiar transversal 

 canal-like fissures were seen to traverse the crystal from both sides, on 

 the pinaeoidal faces, at right angles to the prismatic direction, as 

 shown on the lower half of the crystal in fig. 5, probably corres- 

 ponding to the line of chemical activity. The minute enclosures of 

 Picotite could not be, in any way, removed. The sample thus 

 obtained, was analyzed by Mr. T. Shimizu, to whom I here express 

 my sincere thanks. The result of the analysis is as follows : — 



Si 2 55-04% 



A1 2 3 -88 



Cr 2 3 -49 



Fe 9-40 



MnO -18 



CaO 1-55 



MgO 32-65 



H 2 -45 



100-64 

 Rejecting the small quantities of alumina, lime &c. in the above 

 result, and calculating the rest up to 100, we have : — 



Ox. ratio. 



Si 2 56-69% 30-234 14-05 



FeO 9-68 2-151 1 



MgO 33-63 13-452 6-25 



100-00 

 From this we see that the composition m:iy be represented by 

 FeO. 6 MgO. 7Si0 2 , which is equivalent to Fe Si 3 + 6 MgSi0 3 . 

 This when calculated in percentage gives as follows : — 



Si 2 57-38% 



FeO 9-83 



MgO 32-79 



100-00 



