THE GUEAÏ ERUPTION OF ÖAKüItA-JIMA IN 1914. 



177 



Phcnocrysts Jiro tabular lalmidorite crystals (2 7nm. or less), 

 seriate and zonal structured with difterent extinction-directions, 

 one variety being clear (PI. XIX. Fig. 3), the other being full 

 of glass inclosures (Fig. 4) ; some are corroded and rounded 

 in outlines, and often internally ruptured. Microphenocrysts 

 are pyroxenes, of which the prismatic pleochroic hypersthene 

 (PL XIX. Figs. 0, 7, PI. XX. Fig. 4), octagonal in l)asal section, 

 usnally dominates over anhedral augite,^^ and both are often 

 found in parallel intergrowth only in lai'ger individuals. Grayish 

 apatite occurs as an accessory. The other microphenocrysts are 

 the light greenish -yellow olivine and occasionally magnetite 



clumps, the olivine be- 

 ing never idiomorphic 

 in thc^se fluent lavas 

 (PI. XIX. Fig. 7,0 ; PL XX. 

 Fig. 3). 



The olivine'^ habi- 

 tually forms a nucleus 

 of glomerophyric mass, o,- 

 the outer zone being a 

 divergent mass of hypers- 

 thene prismoids (Text-fig. 

 39, h), and the amoeboid 

 iron ore constitutes a 

 transitional zone. The 

 whole appearance sug- 

 gests the idea that the 



Fig. 39. — Cnxcked olivine core with a rim of 



hypersthene crystals in the land-lava of 



the western field. 



1) The crystal is tabular on the pinacoid (100), and the random sections usiially met with 

 are also the same pinacoidal plane with straight extinction, so that the estimation of the relative 

 amount of both the straightly and obliquely extingiushing pyroxenes is only approximative. 

 PI. XIX. Fig. 8; PI. XX. Figs. 1 an.l 3. 



2) See posted, page 18.5. 



