544 



N. L. BOWEN 



much even of these extreme sediments might be incorporated in an 

 igneous rock without changing its mineralogy. The fact is an 

 obvious deduction from the equilibrium diagram of any investigated 

 three component system and it is equally true of a more complex 

 system. Figure 9 shows the solid phases formed immediately upon 

 complete consolidation of any mixture of CaO, AI2O3 and SiOz. A 

 mixture of composition {A) consists, upon complete consolidation, of 

 anorthite, wollastonite, and gehlenite, one third of each. One may 



3C»0.ESiO2, 

 2C.O.SiO, 



Fig. 9. — Diagram of the system CaO-AljOj-SiOj showing phases formed upon 

 complete consolidation. (After Rankin and Wright.) 



add to this mixture any amount of CaO up to about 15 per cent of 

 itself, without changing the mineral composition of the consoHdated 

 product. Similar amounts of either AI2O3 or SiO^ might be added, 

 the only change in all cases being in the relative amounts of the 

 minerals, not in the kind of minerals. A certain amount of change 

 in the order of separation of the minerals would be effected but the 

 temperature of final consolidation, the composition of the final 

 liquid and the possible differentiates that might be formed by frac- 

 tional crystallization would in all cases remain as before. Only 



