570 W. L. Bowen — The Binary System. 



difference in thermal properties is correspondingly great. Thus 

 it was found by the writer that nephelite from Magnet Cove 

 quenched from 1370° gave only a clear glass and therefore 

 melts at some temperature below 1370°. Moreover, Wright 8 

 has found that molten fc nephelite ' (Magnet Cove) crystallizes 

 directly as nephelite without first showing the carnegieite 

 form. In this respect nephelite from Magnet Cove behaves 

 like the artificial nephelites with 28*5-35 per cent CaAl 2 Si 2 8 

 in solid solution. 



Nephelite Mix-Crystals. — The extreme nephelite mix- 

 crystals with 35 per cent CaAl 2 Si 2 8 contain approximately 7 

 per cent CaO. The lime content of natural nephelites never 

 approaches such an amount. In nature, however, nephelite 

 never occurs in intimate association with pure anorthite, 

 although very often it does occur with a plagioclase. A plag- 

 ioclase is a solution of anorthite in albite just as the mix- 

 crystals above referred to consist of a solution of anorthite in 

 nephelite. When all three substances are present there is, 

 theoretically, a definite distribution ratio of anorthite between 

 albite and nephelite, this ratio being equal to the ratio of 

 solubilities. Albite dissolves anorthite to an unlimited extent. 

 Nephelite dissolves 35 per cent. We have 



■§= =K= 5 ^ ro =3(approx.) 



where C,= concentration of anorthite in the plagioclase. 

 C 2 = concentration of anorthite in the nephelite. 



Obviously only when C x =l (i. e. pure anorthite) will 

 C 2 = 35/100. For every other plagioclase there corresponds a 

 definite composition of nephelite in equilibrium with it and 

 the concentration of anorthite in plagioclase is three times that 

 in the nephelite. The natural minerals always contain import- 

 ant quantities of other molecules which introduce variations, 

 and viscosity may be such as to inhibit equilibrium, but the 

 distribution should probably be of the order indicated. The 

 analysis of a nephelite from Vesuvius shows the highest lime 

 percentage (2*20 per cent) (11 per cent CaAl 2 Si 2 8 ) of all 

 analyses of that mineral that have been made with sufficient 

 care to warrant their consideration. 20 This nephelite should 

 be in equilibrium with a plagioclase of approximate composi- 

 tion AbgAn^ 



Other Solid Solutions. — The zeolite, thomsonite, consists of 

 CaAl 2 Si 2 8 with Na 2 Al 2 Si 2 8 U P to 50 per cent, and corre- 

 sponds in composition with some of the writer's mixtures with 

 the addition of water. If, as Zambonini 21 concludes from the 

 result of experiments, thomsonite is not a definite hydrate, the 



