FOYAITE-IJOLITE SERIES OF MAGNET COVE 



6il 



Apart from the determination of minor constituents, my 

 analysis (i) does not differ materially from that of Brackett 



I. Foyaite, Diamond Jo quarry, Magnet Cove. Washington, analyst. 

 II. Foyaite, same locality. Brackett and Smith, analysts. Williams, Sp. gr. 2.599 

 at 26°C., op. cit., p. 238. 



and Smith (11), except in the presence in the latter of nearly 

 2 per cent, of pyrite, and in the alkalis, I gives a ratio of 

 NagO: KgO of 1.3, while in II it is 1.92. The amount of BaO 

 in I is high, and is noteworthy since it is found only in traces 

 or not at all in the other rocks. It probably belongs with the 

 abundant orthoclase, since other cases are known of BaO par- 

 tially replacing K3O in the feldspar of alkaline rocks. The 

 analysis calculates out thus : 



Orthoclase - 51.8 



Nephelite - - 20.3 



Cancrinite - 13.1 



Aegirite - - 5.7 



Diopside - - 8.6 



Titanite and pyrite - 0.5 



100. o 

 It is seen that this bears out Williams's remark that " the 

 orthoclase is perfectly free from isomorphous mixtures of other 

 feldspars." It is indeed somewhat remarkable that the albite 

 molecule should be entirely lacking, or almost so, in a rock 

 containing so much soda. It seems to be characteristic of the 



'FeSa. 



