422 Andersen — System Anorthite-Forsterite-Silica. 



redissolve and clinoenstatite to crystallize out. This reaction 

 goes on as long as there is any liquid left, the temperature and 

 the composition of the liquid remaining constant throughout. 

 When the reaction is completed, and all liquid used up, there 

 is still some forsterite left, and a solid mixture of forsterite 

 and clinoenstatite results. Pure MgSi0 3 melts behave exactly 

 as described, but the last of the liquid and the last of the 

 forsterite are here used up at the same time. The final crys- 



Fig. 1. 



D< 



\ 























X. 













































FORSTE 



RITE 





















a 





\ 





*% 



' -^ 













600 



LIOU 







\ 



/ 



















— e 



e\ 



*?/ 





CRISTOBALITE 



ft 



LIQUID 







FC 



3RSTERITE 



a 



G 



— 

















CL 



! 

 NO-ENSTATITE 

 L 





CLINO- 



IN^TATITE 



& 



CRISTO 



BALITE 





400 





1 

 1 

















MgSiO. 



WT PER CENT 



Sip. 



tallization product, therefore, is pure clinoenstatite. Between 

 E and F (mixtures between pure En and En 97*5, Si0 2 2*5) 

 forsterite is still the primary phase, and the reaction at point 

 F takes place as before described with simultaneous solution of 

 forsterite and crystallization of clinoenstatite. When, how- 

 ever, the reaction is complete, all forsterite is redissolved while 

 there is still some liquid left. The crystallization continues 

 along the line F G with separation of clinoenstatite. At point G-, 

 the eutectic clinoenstatite-cristobalite, the rest of the liquid, 

 solidifies w T ith simultaneous crystallization of clinoenstatite and 

 cristobalite. In mixtures richer in silica than G, cristobalite 

 crystallizes as primary phase, and when G is reached there is 

 again eutectic crystallization of cristobalite and clinoenstatite. 



The System Anorthite- Silica. 



The anorthite-silica mixtures form a true binary system of 

 simple type. The results of the quenchings are contained in 

 Table 2. The equilibrium diagram is represented in fig. 2. 



