TEE BEHAVIOR OF INCLUSIONS IN IGNEOUS MAGMAS 549 



The phases capable of formation from the original unchanged 

 magma are: 



Phase Mineral molecules represented 



Olivine Mg2Si04+Fe.Si04 



Magnetite FeO.Fe203 



Plagioclase CaAUSiaOg+etc. 



Pyroxene CaMgSi306+MgSi03+AlA*+CaFeSi206+ 



FeSiOa+FeA* 



*0ften written as existing in the Tschermak molecule, for which there is no good reason. See 

 Washington and Merwin, Amer. Jour. Sci., Vol. Ill (ig22), p. 121. 



Upon addition of CaO the following principal adjustments in the 

 proportions of these mineral molecules may occur without the 

 appearance of new phases : 



GaO+ 2FeSiO,+FeA = CaFeSi^Oe+FeO . Fe A ; 

 CaO+3MgSi03 = CaMgSi206+Mg2Si04; 

 CaO+ Al203+4MgSi03 = CaALSi208+ 2Mg2Si04. 



Upon addition of SiOz: 



SiO.+Mg.Si04- aMgSiOj; 

 Si02+AL03+CaMgSi206=CaALSi208+MgSi03. 



Upon addition of kaolin, which we may regard as AlaSiOg-l-SiOa, 

 with SiOz having the same effect as above: 



Al2SiOs+CaMgSi206=CaAl3Si208+MgSi03. 



The results may be put in words by stating that addition of lime 

 tends to increase the amount of magnetite and olivine, to make the 

 pyroxene more nearly a pure diopside-hedenbergite and to increase 

 the anorthite content of the plagioclase. The addition of silica 

 tends to decrease the amount of olivine and to increase the mag- 

 nesian content of the pyroxene and the anorthite content of the 

 plagioclase. The addition of kaolin tends to increase the amount of 

 magnesia in the pyroxene and of the anorthite in the plagioclase. 



In the case of superheated magma the added material might be 

 directly dissolved and upon solidification the adjustments noted 

 would appear in the crystalline phases. In the case of saturated 

 magma the phases noted would be developed by reaction with the 

 added material and at the same time a further amount of them 

 would be precipitated from the liquid. In neither case would the 

 course of crystallization be fundamentally changed since crystalliza- 



