THE BEHAVIOR OF INCLUSIONS IN IGNEOUS MAGMAS 555 



sillimanite, spinel, and liquid; and at still lower temperatures, of 

 sillimanite, spinel, and cordierite. 



It should be realized that these conditions we have pictured as 

 occurring about sillimanite inclusions are transient states. We may 

 deduce from an equilibrium diagram the condition of a certain layer 

 about an inclusion, but the system as a whole is not in equilibrium 



S1O2 



MgO-Si02j 



Fig. 12. — Equilibrium diagram of the system MgO-ALO^-SiO^. (After Rankin 

 and Merwin.) 



since there are composition gradients about these inclusions. 

 Nevertheless this changing state might become fixed and be revealed 

 as a result of complete consolidation of the mass. 



The actual magma by which the schist inclusions were attacked 

 may be regarded as showing the combined effects of the anorthite 

 liquid and the magnesian liquid of the experimental systems. It is 

 true the magma did not correspond definitely with any such mix- 

 ture of anorthite and magnesian silicate, but it was closely related, 

 consisting mainly of plagioclase and magnesian silicates, and its 

 effect on sillimanite-rich inclusions might reasonably be similar. 



