222 W. T. Schaller — Dumortierite. 



The best series of analyses is that by Ford from three Amer- 

 ican localities. His first analyses of the Arizona mineral are : 



Si0 2 



A1 2 G 3 



FeO .... 



1 



30-00 



63-20 



-23 



2 



29-66 



63-74 



•23 



5-06 



1-38 



3 

 29-91 

 63-76 



Average. 

 29-86 

 63-56 

 •23 



BO 



5-47 



5-26 



2 3 



H 



1-45 



1-41 



2 







10032 

 The ratios calculated from the average analysis gives : 



Si0 2 6-29 or 6 X 1'05 



A1 2 3 _. 7-94 8 X -99 



B 2 3 -96 1 X -96 



H 2 _. 1-00 1 X 1*00 



The agreement with the proposed formula is perfect. 

 His second analysis, that of the California mineral, shows 

 slight variations from the results obtained by the writer. The 

 presence of titanium was not determined. His analysis is : 



Eatios. 

 6-17 or 6 X 1*03 



7'40 8 X '93 



Si0 2 



30-58 



A1A---- 



61-83 



Fe 8 3 --- 



-36 



B 2 3 



5-93 



HO 



2'14 



•"-2 





1-04 1 X 1'04 



1-45 1 X 1*45 



100-84 

 The ratios agree well with the new formula except for the 

 water content. Remembering, however, that the amount of 

 water present is very small and that a difference of *10 per 

 cent would make a large difference in the ratios, that Ford deter- 

 mined his water by igniting the mineral with lime, thus not 

 weighing the water directly, and that the writer obtained only 

 1-52 per cent on the same mineral from the same locality, it 

 seems much more preferable to regard the determination of 

 the water in Ford's analysis as too high rather than to attempt 

 an explanation of it by the assumption of " isomorphous replac- 

 ment, etc." 



Of the third analysis by Ford, of the New York mineral, he 

 says : " It is fully realized that the results are not to be looked 

 upon as being as exact as those of the other analyses." His 

 analysis is : 



Eatios. 



Si0 2 31-24 6-23 or 6 X 1'04 



A1 2 3 6126 7*23 8X *90 



Fe 2 0, -10 



B 2 3 *_. 6-14 1-06 lXl'06 



H a O 2-09 1-40 1X1*40 



100-83 



