178 N. L. Bowen — Crystallization of Haplobasaltic, 



crystals. Similarly the point K on the straight line EEK 

 represents the composition of the plagioclase in the latter case. 

 This method is the only one applicable to the determination of 

 the composition of the plagioclase crystals in equilibrium with 

 any liquid in the plagioclase field (i. e., not on the boundary 



ao WT. PER CENT 



G eo 



. . ,. . REFRACTIVE INDEX X. 



DETERMINED POINTS TEMPERATURE 



ANORTHITE 



Fig. 12. Isotherms and isofracts. 



Curve, in which case the three-phase-boundaries fix the com- 

 position of the plagioclase) for the crystals themselves are too 

 small for precise optical determination. 



Crystallization Curves in the Plagioclase Field. — With the 

 aid of the foregoing determinations of the composition of the 

 liquid two representative crystallization curves in the plagio- 

 clase field can be drawn and the crystallization of the mixtures 



