PROP. J. H. L. VOGT ON LABKADOPvITE-STORITE [May 1909, 



Epi-Hp, an( i Em-ep ar e the binary eutectics (in the drawing they 

 are rather arbitrarily placed) between plagioclase and magnetite, 

 plagioclase and hyperstbene (or pyroxenic mineral), magnetite 



and hypersthene (or 



Pig. 3. X^yroxenic mineral) ; 



Efi. M and E Pi-M-s P is the 



7 ternary eutectic 



M point. 



P represents the 

 composition of the 

 original soiution(72'8 

 per cent. PI, Q-b per 

 cent.M,20-7percent. 

 Up). The crystalli- 

 zation of the plagio- 

 clase alone — in the 

 phenocrysts, to the 

 amount of 23 per 

 cent, of the original 

 solution — takes place 

 along the curve 

 P— Q ; and at 

 Q the simultaneous 

 crystallization begins of plagioclase and magnetite, along the curve 

 Q — Epi-M-Hp- As there are in the present case two pyroxenic 

 minerals, the simple ternary diagram is not applicable to the final 

 crystallization. 



The composition of the point Q is found from Analysis 4, 

 eliminating the small admixtures of biotite, spinel, etc. and re- 

 calculating the rest to 100 per cent. "We shall then obtain the 

 following mixture : — 



64-5 per cent, of plagioclase. 



8'8 per cent, of magnetite (Fe 3 4 ). 

 27 '0 per cent, of hypersthene-diallage. 



This composition tells us that with more plagioclase-component 

 in the solution plagioclase crystallizes first ; with more magnetite- 

 component in the solution, on the other hand, magnetite crystallizes 

 first. By similar investigations in the future, we shall, without 

 doubt, succeed in fixing a whole series of such points on the eutectic 

 lines. The investigation will be complicated, however, by the 

 presence of so many components, especially among the pyroxene- 

 minerals. 



The composition of the point Epi-m-hp with diallage or hyper- 

 sthene may be called 'the ternary gabbroidal eutectic.' 

 If the composition of this point be determined, we shall travel far 

 along the way to the study of the sequence of crystallization in 

 gabbroidal magmas. 



On the equilibrium between the solid and the liquid 

 anorthite + albite-phase. — According to the analytical 



