Volcano üshima, Idzu. 117 



of the crystals, however, had an opportunity to sink in company 

 with the oUvine crystals. 



Very slow cooling (Formation of i>lienocrysts) Very rapid 



cooling 



.(-Mg-rich Fe-rich-* (Formation 



1 of grouudmassj 



Olivine » "~ 



Plagioclase 



Hypersthen» 



Augite 



Mt^netite 



An- rich Ab-rich -^ 



AbiöAnss i 



I- 



t 



I 



Fig. 40. Diagram showing the order of crystallization. 



(Ill) The Third Stage. 



Olivine — The separation of olivine was completed and the 

 later formed crystals comparatively rich in fayalite were in the act 

 of sinking. As a result of the removal of olivine from the magma, 

 an excess of silica was brought about in the residual liquid. 



Plagioclase, — The plagioclase crystals were separating and 

 their composition w^as becoming gradually sodic. 



Pyroxenes. — The crystals of hypersthene appeared, but the 

 duration of their crystallization was brief whereupon augite began 

 to separate. Hypersthene and augite being heavier than the magma, 

 sank in it. 



(IV) The Last State in the Magma Basin. 



The crystallization of the magma in the intratolluric stage 

 proceeded as above, while tlie magmatic temperature became deci- 



