Haplodioritic and Related Magmas. 



175 



(AbjAn, 50 per cent-diopside 50 per cent) begins to crystallize 

 at 1275°, diopside separating and the liquid changing along the 

 straight line AFG towards G. At 1235°, when the liquid has 

 the composition G, plagioclase of composition H (Ab,An 4 ) 

 begins to crystallize, the point JBL being determined by the 

 three-phase-boundary (GH) through G. As the temperature is 

 lowered the composition of the liquid follows the boundary 



ALBITE T a»,a«, L R H ANORTHIT6 



Fig. 11. Crystallization of mixtures in diopside field. 



curve towards M. At 1218°, when the liquid has the composi- 

 tion K, the plagioclase has changed in composition from 

 H(Ab 1 An 4 ) to L(Ab 1 An 2 ). Finally at 1200° the liquid is used 

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

 plagioclase having now changed in composition to AbjAn^Z). 

 MZ is the three-phase-boundary through the composition 

 A^Anj and fixes at the point M the temperature of final con- 

 solidation of F or of any other mixture of Al^An, and diop- 

 side. 



The mixture X(Ab.An, 60 per cent-diopside 40 per cent) 

 begins to crystallize at 1252° with the separation of diopside, 



