Andersen — System AnortJiite-Forsterite-Silica. 445 



For mixtures within g L M the reaction at M results in 

 clinoenstatite, anorthite and liquid and the crystallization pro- 

 ceeds to N, where the eutectic mixture anorthite, clinoensta- 

 tite, silica is formed. 



The crystallization of mixtures within the field D M E will 

 be illustrated by discussing (fig. 11) the crystallization curves 

 of some particular mixtures.* Three mixtures are selected : Jc 

 on the forsterite side of the conjugation line anorthite-enstatite ; 

 I on this line itself and m on the silica side of the line. The 

 course of crystallization of h will be as follows : Along h n 

 crystallization of forsterite ; from n to M solution of part of 

 the forsterite and simultaneous crystallization of clinoenstatite ; 

 at M continued reaction with solution of forsterite and crys- 

 tallization of clinoenstatite and anorthite until all is solid, con- 

 sisting of forsterite, clinoenstatite and anorthite. 



This type of crystallization curve is represented in Table 8, 

 showing the phase relations at the principal stages of crys- 

 tallization of a melt of composition An 25, Fo 60, SiO, 15. 



Table 8. 



Illustrating the crystallization of a mixture 

 An 25, Fo 25, En 50 (type k fig. 11). 





Amount present in weight per cent of the initial mixture. 





1 



2 



3 



3-2 



Phase 



When crys- 

 tallization 

 reaches n 



When crys- 

 tallization 

 reaches M 



When solidi- 

 fication at M 

 is completed 



Showing 

 amount of crys- 

 tallization and 

 dissolution at M 



Liquid 

 Forsterite 

 Clinoenstatite 

 Anorthite 



63 



3V 

 

 



45 



34 



21 









 25 

 50 

 25 



— 45 



— 9 



+ 29 

 + 25 



For the mixture I the steps in the course of crystallization 

 are the same : Along I n forsterite crystallizing ; along n M 

 forsterite redissolved, clinoenstatite crystallizing out ; at M 

 anorthite and clinoenstatite crystallizing, forsterite dissolving. 

 The final solid product now, however, consists of clinoenstatite 

 and anorthite only. 



In the last of the three mixtures, m, the crystallization 

 again follows the line m n with separation of forsterite, the 

 line n M with simultaneous solution of forsterite and crystalli- 

 zation of clinoenstatite, and the reaction at M goes on with 

 solution of forsterite and crystallization of clinoenstatite and 



* See footnote, p. 443. 



