Volcano Üshima, Mza. 



99 



Olicine is traversed by namerous cracks. It is (Fe.SiOi)i:2-i8 

 (Mg.,SiOj88-s2 with the refractive indices : — 



a<1.636<.3<1.687<r 

 Observed injixinium refractive iudex < 1.7185 



Small interstices between the large individuals of the minerals 

 are filled with a material containing hypersthene, similar to the 

 groundmass of the lava. 



14) Augite-micro-diorite. (PI. VI. Fig. 6.) 



An ejected block of rather acidic nature was found at the 

 northern foot of Kagamiliata'^ (Ic) imbedded in the uppermost bed 

 of agglomerate. 



It is a holocrystalline, fine-grained (mostly 0.3-1.5 mm. in 

 diameter) mass of hypidiomorphic granular texture, consisting 

 essentially of plagioclase and augite with magnetite and apatite as 

 accessories. 



Plagioclase belongs to andesine-labradorite with chemical 

 compositions ranging from Ab,i,An,, to Ab^^An^g, determined by 

 the refractive indices (1.55-1.56). These plagioclases are twinned 

 simply (Carlsbad law) and polysynthetically (albite law) and exhibit 

 n 1 i c e a b 1 e z n a 1 s t r a c t u r e s . In the simplest case the innermost 



zone is the most calcic. 



m 



f? 



ill 



Fig. 39. 



Most calcic. 

 More soflic. 



2. Less caliüe. 

 i. Most sodic. 



successive ones become 

 more and more sodic with 

 gradual transition ; while 

 not a few show the more 

 complex manner of zoning 

 as shown in Fig. 39. 



1) 



