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JOURNAL OF GEOLOGY— SUPPLEMENT 



and plagioclase continue to separate and the plagioclase crystals, 

 not only those separating at any instant, but also those which had 

 formerly separated, continually change in composition — become 

 richer in albite. At 1220° the whole mass is made up of 37 per cent 

 diopside crystals, 25 per cent labradorite crystals of composition L 

 (AbiAua), and 38 per cent liquid of composition K. As the tem- 

 perature falls still lower the liquid gradually decreases in amount 



Fig. 8. — Crystallization curves for the system: diopside, plagioclase 



and continually changes in composition until at 1200° it is all used 

 up, the last minute quantity having the composition M. In the 

 meantime diopside and plagioclase crystals have been separating 

 and the plagioclase has been changing continuously in composition 

 until at 1 200°, when the last of the liquid disappears, the composi- 

 tion of the feldspar is AbiAui. The whole mass now consists of 

 50 per cent diopside and 50 per cent AbiAui. 



