414 



bowen: anthophylIvITE 



given above are in accord with those observed in the pure arti- 

 ficial mineral and in another natural anthophyllite whose AI2O3 

 content is low enough to admit comparison. The relation be- 

 tween refractive indices and FeSiOa content is shown in table 

 I and graphically in figure i. 



TABLE I. — Chemical Composition and Optical Properties of Anthophyllite. 



Si02 



AI2O3 



FeO + MnO 15 04 



MgO 



7 



^ 



° Michel-Lew and Lacroix, Les Mineraux des Roches, p. 150. 



The indices given for the artificial kupfferite are redetermined 

 values and are slightly higher than those given in an early paper 

 from this Laboratory.^ The artificial material is not very 

 satisfactory for index determination, but the above values are 

 observed when grains are used that are free from the dusty 

 effect produced by contamination with excess silica/ 



* Allen, Wright and Clement. Amer. Journ. Sci. 22: 410. 1906. 



* Bowen and Andersen. Amer. Journ. Sci. 37: 492. 1914. 



