•• 







Mineralogy and Geology. 273 



chloritoid, in which water was an essential ingredient, gave as the re- 

 sult of his analysis, 



*•* ••• ••• 



(Fe, Mg) 3 Si-f- A12 Si-f3H ; 



t • » # * - 



ALSiandH 



for which he adopted the ratio 3:6:6:8. Rammelsberg has taken the 

 ratio as 3:6:5:2, and gives for the formula of this mineral 



*■• • • ■ m r t 



which requires 



3R3Si+2Al 3 Si-f6H, 



9 f * 



Al 23-61, Fe 85-31, H 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, 



• r + t f ft 



Fe 3 Si+Al 3 Si. 



The substance analyzed by Erdmann did not contain water, and 

 there seem to be two distinct substances, one of which is a hydrous sil- 

 icate, and the other anhydrous. That the analysis of Bonsdorff was 

 probably correct, is shown by the following analysis of the mineral de- 

 scribed by Jackson as Masonite, which I find to have the same compo- 

 sition as the chloritoid of Bonsdorff, which it closely resembles in ex- 

 ternal characters. 



The results of an analysis of Masonite were as follows : 



Oxvn* n. Ratio. 



[ Silica 28-27 14-55 3-2 



Alumina . . . . 32- 16 1502 33 



Protoxyd of iron . , . 3372 4-49 1-6 

 Magnesia . . . -13 



Water 5 00 444 1- 



99-28 



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



will be 



• . . ••• ' •• 



Fe- Si+Al 2 S1+2H, 



*hich is that given by Bonsdorff for chloritoid, with one atom of water 

 •ess, 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. 

 The formula given above requires 



• - • 



* i 



Si 28-56, Al 3206, Fe 3360, H 5-60=100-02. 



This, it will be seen, agrees very nearly with the results of analysis ; 



would therefore suggest that the name of Masonite should be retained 



| for the hydrous chloritoid, as the formula given by Erdmann has been 



generally adopted for what is supposed to be the real chloritoid. 



2- Black Oxyd of Copper of Lake Superior; (lb., p. 102.)— Mr. 

 Whitney made some remarks on the remarkable vein of black oxyd of 



Second Sertes, Vol. VIII, No. 23.— Sept., 1849. 35 



