444 Andersen — System Anorthite-Forsterite-Silica. 



In mixtures along the line A L (part of the conjugation line 

 anorthite-enstatite) the crystallization takes place in the same 

 way, but when the reaction at the point M is complete, the 

 forsterite and the liquid have both been used up at the same 

 time and there is left a solid mixture of anorthite and clino- 

 enstatite, as if there had been a eutectic crystallization of these 

 two phases. If, on the other hand, the mixture has a com- 

 position within the field ALM the forsterite will be the first 

 phase to disappear when the reaction at M is complete, and the 

 remaining liquid will crystallize along the line M N with 

 simultaneous separation of anorthite and clinoenstatite, until 

 the point N, the ternary eutectic, is reached, where anorthite, 

 clinoenstatite and silica finally crystallize out together. 



In all mixtures within the field DKMF forsterite is the 

 primary phase. The second step of crystallization depends on 

 the location of the mixtures within the different subdivisions 

 of the forsterite field. Within the field DKM, the second 

 and third steps of crystallization will be exactly like those of 

 the corresponding mixtures on the anorthite side of the line 

 K M described above : simultaneous crystallization of forster- 

 ite and anorthite along K M and reaction at M resulting in 

 decrease of forsterite and liquid and crystallization of clino- 

 enstatite together with anorthite. The final result of the reac- 

 tion, whether the forsterite or the liquid is first used up, again 

 depends upon the original composition of the mixture. In 

 mixtures within the field D^LK there will be forsterite left 

 after the reaction and the result is complete solidification at M 

 of a mixture of forsterite, anorthite and silica. The result of 

 the crystallization of mixtures on the line g L (part of the con- 

 jugation line anorthite-enstatite) will be the same as described 

 for the mixtures L A : complete solidification at M of a mix- 

 ture of anorthite and clinoenstatite. The principal stages in 

 the crystallization of a mixture of composition An 46, En 54 

 (point g figs. 9 and 11) are represented in Table 7. 



Table 7. 



Illustrating the crystallization of a mixture 



An 46, En 54 (g figs. 9 and 11). 





Amount present in weight per cent of the initial mixture. 





1 



2 



2-1 



Phase 



When crystalliza- 

 tion reaches M. 



When solidifica- 

 tion at M is com- 

 pleted. 



Showing amount 



of crystallization 



and dissolution 



at M. 



Liquid 

 Forsterite 

 Anorthite 

 Clinoenstatite 



84 



16 

















 46 

 54 



— 84 

 -16 



+ 46 



+ 54 



