110 



schaller: composition of nephelite 



AlNaSi0 4 , has been prepared artificially, and Washington and 

 Wright have assumed 2 its presence to the extent of 5.58 per cent 

 in a feldspar (anemousite) consisting essentially of albite and 

 anorthite in isomorphous mixture. 



We have, in the feldspars just named, two types of compounds, 

 A1R / Si0 4 and A.lR'Si 3 08, and their isomorphous relation, as earlier 

 developed by Clarke (Bull. 125, U. S. Geol. Survey) lead to a 

 simple interpretation of the composition of nephelite. These 

 compounds occur in several modifications, which are isomorphous. 

 This relation can be best shown schematically. 



Modifications of Compounds AlR'Si0 4 and AlR'Si 3 O s 



The mineral nephelite is then an isomorphous mixture of the 

 compounds crystallizing in the hexagonal modification, which 

 are: 



AlNaSi0 4 — essential component 



AlKSi0 4 — kaliophilite 



AlNaSi 3 Os — best known in its triclinic form as albite. 



To show that the explanation offered is in agreement with the 

 analyses of nephelite it will suffice to quote two analyses, the first 



2 Washington, H. S., and Wright, F. E.: A feldspar from Linosa and the exist- 

 ence of soda anorthite (Carnegieite). Amer. Jour. Sci., 29: 52. 1910. 



