THE MINERALOGRAPHY OF THE FELDSPARS 



29s 



more data are not forthcoming; for it is truly surprising to find 

 that while many analyses are available, the values of the specific 

 gravity are only occasionally given. In drawing conclusions from 



TABLE II 



Recast of Hypoperthite, San Diego Coxjnty, California 



AVERAGE 



Per Cent 



Orthoclase or Microcline §5-35 



Albite 5 . 80 



Anorthite 2.25 



Nephelite 6 . 60 



such miscellaneous data we must remember that the chemical 

 analyses of today are vastly superior to those collected and pub- 

 lished by Dana, Hintze, Doelter, Herzenberg and others.^ The 

 chemical analyses were recast into terms of three components, 



^ See H. S. Washington and H. E. Merwin, Anier. Jour. Sci. (5), I (1921), 20. 

 Larsen says {U.S. Geol. Surv. Bull. 67Q [1921], p. 6): "Much further work on the 

 optical constants and more complete and accurate data on nearly all the minerals are 

 needed .... a highly accurate determination of physical properties [etc.] of a 

 mineral is of comparatively little value unless the data obtained are definitely tied to 

 a chemical analysis." See Arthur Holmes, Petrographic Methods and Calculations. - 



