Andersen — System Anorthite-Forsterite-Silica. 437 



considered in terms of the ternary system. These mixtures 

 are those represented by points within the field B C K in the 

 ternary diagram, fig. 9. The significance of the points B and 

 C has already been discussed. K is the point where the spinel 

 field meets the boundary curve forsterite : anorthite. The 

 point K has been determined at the composition An 61, Fo 



Fig. 9. 



CRISTOBALITE 



<=U No _ 



MgSiO, 



fSTATn 



FORSTERITE 



%, 



Lk ^ - - 



29-5, Si0 2 9-5, and the temperature 1320°. The lines B K 

 and C K have a similar significance in the ternary system as 

 the points B and C in the binary system anorthite-forsterite. 

 Mixtures within the field A B K will crystallize with anorthite 

 as primary phase and when a point on the curve B K is reached 

 spinel begins to crystallize. In mixtures within the field D 

 C K forsterite is the primary phase and when the crystalli_ 

 zation reaches the line C K spinel is also here separated. I n 



