THE BEHAVIOR OF INCLUSIONS IN IGNEOUS MAGMAS 519 



characteristic molecules of basic rocks, mix in the liquid state with 

 evolution of heat, whereas albite, one of the most characteristic 

 molecules of acid rocks, mixes with diopside in the liquid state with 

 absorption of heat and with anorthite without significant heat effect. 



Can<jJi.^O^ ma/ percenT va/i/JijC^ 



Fig. 4. — Equilibrium diagram of diopside and albite. Determined curves in 

 full lines. Broken curve calculated on the assumption of no mixing heats. 



These results are quite the opposite of what is often assumed to be 

 the case. Many statements are to be found in the literature to the 

 effect that acid and basic rock material will mix with evolution of 

 heat. There is nothing in the results of studies of phase equilibrium 



CatlgJi/?^ rno/ per cent /i/aAISi^Og 



Fig. 5. — Curve of integral mixing heats of diopside and albite 



to warrant such a statement; indeed, there are, as we have seen 

 above, good reasons for doubting it. 



Possibly in rare cases, where more fundamental reactions are 

 involved, greater heats of mixing are available, but the mixing of 

 two liquids has, in itself, little importance in petrogenesis. Our 

 particular interest lies in the heat effect on mixing solid rock-matter 



