101 



7.88 : 16.61 : 14.27 ; 6.17, for which he adopted the ratio 



3:6:6:3. Rammelsberg has taken the ratio as 3 : 6 : 5 : 2, 



and gives the formula of this mineral as 



3 Rs Si + 2 A13 Si + 6 H, 



which requires 



Silica 25.18 



Alumina 33.61 



Protoxide of iron 35.31 



Water 5.88 



99.98 

 Erdmann has analyzed a mineral supposed to be the chlorite- 

 spar or chloritoid described by Fiedler, and gives as the result of 

 two analyses, agreeing closely with each other, the formula, 

 FeS Si + AF Si. 

 The substance analyzed by Erdmann did not contain water, 

 and there seem to be two distinct substances, one of which is a 

 hydrous silicate, and the other anhydrous. That the analysis of 

 Bonsdorff was probably correct, is shown by the following 

 analysis of the mineral described by Jackson as Masonite, which 

 I find to have the same composition as the chloritoid of Bons- 

 dorff, which it closely resembles in external characters. 

 The results of an analysis of Masonite were as follows : 



99.28 



The ratio of Si, Fe, Al, and H, being nearly 6:3:6:2, 

 the formula will be 



Fe3 Si + A12 Si + 2 H, 



which is that given by Bonsdorff for chloritoid, with one atom of 

 water less, which we may easily conceive to have been stated 

 too high, if the mineral had not been carefully dried, especially 

 as there is an excess of 1.6 per cent, in the analysis. 



