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N. L. BOWEN 



crystals if we examine the crystallization of mixtures of the system 

 — diopside, anorthite, albite — not because proportions will be the 

 same, but because they will be rather of the same order in the 

 natural system and will aid us in deciding whether the process is a 

 reasonable method of producing anorthosites as we find them. 



ANORTHITE 



Fig. i. — Diagram of crystallization in plagioclase-diopside melts 



A liquid of composition F (Fig. i), which contains 50 per cent 

 diopside and 50 per cent labradorite (AbjAnj), begins to crystallize 

 at 1275 , diopside separating first. As the temperature falls the 

 composition of the liquid changes from F along AFG (directly away 

 from diopside) , and when the temperature 1235 is reached the mass 

 consists of 17 per cent diopside crystals and 83 per cent liquid of 

 composition G. At this temperature bytownite of composition H 

 (approximately AbjAn 4 ) begins to crystallize and the composition 



