LATER STAGES OF EVOLUTION OF IGNEOUS ROCKS 35 



series, between the two types of crystallization, that in which 

 perfect equilibrium is obtained and that in which zoning occurs/ 

 Crystallization with perfect equilibrium. — A Liquid of composi- 

 tion F (Fig. 8) which contains 50 per cent labradorite (AbiAni) and 

 50 per cent diopside begins to crystallize at 1275°, diopside separat- 

 ing first. As the temperature falls the composition of the liquid 



ALBITE '" ww.^tHctN. -^ =- ANORTHITE 



Fig. 7. — Equilibrium diagram of the system: diopside, plagioclase 



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 Hquid of composition G. 

 At this temperature bytownite of composition H (approximately 

 AbiAn4) begins to crystallize and the composition of the Kquid 

 changes along the boundary curve DE toward D. Both diopside 



^ These correspond with "Erstarrung zweiter Art" and "Erstaming erster Art" 

 respectively of Schreinemakers {Zs. phys. Chemie, L [1905], 189-90). 



