iT. L. Bowen — The Binary System. 551 



Art. XLVL— The Binary System : NaMfii^O^ Nephelite, 

 Carnegieite) — CaAl 2 Si 2 O e (Anorthite) ; by N. L. Bowen.* 



Contents : 



Introduction. 

 Preparation of Materials. 

 Preliminary Study. 

 Heating Curves. 



Method. 



Eesults— Table I. 

 Quenchings. 



Method. 



Eesults -Table II. 

 Equilibrium Diagram. 

 Discussion of Equilibrium Diagram. 

 Optical Study. 



Properties of Anorthite. 

 Carnegieite. 

 Nephelite. 

 Solid Solutions. 

 Work of Earlier Investigators. 



Carnegieite. 



Nephelite. 



Anorthite. 

 Application to Natural Minerals. 



Anorthite. 



Nephelite 



Nephelite Mix-Crystals. 



Other Solid Solutions. 



Carnegieite. 

 Thermometry. 

 General. 



Introduction. 



The study of the system Na 2 Al 2 Si 2 8 — CaAl a Si 2 8 was 

 undertaken because of the very considerable importance of 

 these compounds as rock-forming constituents. 



The compound CaAl 2 Si 2 3 occurs in nature as the mineral 

 anorthite. The preparation of anorthite in the laboratory has 

 been accomplished by a number of workers. 



The compound Na 2 Al 2 Si 2 8 (NaAlSi0 4 ) approximates in com- 

 position the natural mineral nephelite and has been prepared in 

 a form resembling that of nephelite. It is mentioned in text- 

 books of mineralogy as artificial soda-nephelite and is given a 

 place in order to bring out the chemical relationship within the 

 hexagonal group of which nephelite is the best known member. 



Preparation of Materials. 



In the preparation of mixtures for exact thermal work, it is 

 important that only the purest material should be used. The 

 calcium carbonate was of tested purity, the alumina was freed 



* Presented in partial fulfillment of the requirements for the degree of 

 Doctor of Philosophy in the Department of Geology at the Massachusetts 

 Institute of Technology ; May, 1912. 



