454 S. Weichnan — Irving ite, a New Variety of Lithia-mica. 



Molecular ratios 



6— SiO„. 



1— A10 3 



360 



102-00 

 47-1 

 31-00 

 30-00 

 6-00 

 24-00 



Per cent 



60-00 

 17-00 



(1RO . - 



7-83 



2^ ^Na„0 



( lLi„0 



, \ m 



5-17 

 5-00 

 1-00 



VfF 2 - 



4-00 



600-00 100-00 



Prof. Clarke lias pointed out that the ratios in this lithia- 

 mica are very near B/ 2 AlX(F.OH), in which X represents the 

 acid radicals Si 3 O g and Si0 4 , in the ratios of 4 : 1. According to 

 the view of Clarke, regarding all the OH as F, it could be written 

 thus: 4E / a Al.Si,0 8 F+lR' s Al.Si0 4 F. The true formula is prob- 

 ably some multiple of this expression as previously stated bv 

 Clarke* 



* F. W. Clarke, U. S. Geol. Survey, Bulletin 125, p. 48. 



