74 Vol. XLIIL, Art. 6. — S. Tsuboi : 



Ofcber plienocrystic minerals are pyroxenes, only in a subordi- 

 nate quantity. Of these, subhedral prismatic crystals of hyperstheiie 

 greatly predominate over those of light greenish aur/ife in which 

 6'AZ^43°. The latter are often found surroundhig the former in 

 thin shells in parallel intergrowtli. 



The following optical properties of hypersthene were 

 observed : — 



a < 1.6906 1.6906 <i3< 1.7146 1.7014 < j- 



2F:==85° supposiug ^9 = 1.7 Opticjil cliaiTifter . . ..negative. 



Pleochroism is not strong: — 



X . . . light reddish broMii 

 Y . . . light reddish yellow 

 Z . . . light bluish gi'eeD. 



The above optical properties of hypersthene are comparable to 

 those of tlio mineral from Labrador containing 10^ of FeO, which 

 was studied by Levy and Laceoix. The Labrador specimen has 

 the refractive indices : — 



«=1.692 ;9=1.702 ;-=: 1.705 



The groimdmass is percrystaUine and centimillimeter-grained, 

 and consists of prismoid crystals of labradorite (Ab,,nAu,„), an- 

 hedral light greenish augite, and isometric magnetite, with only 

 a trifling amount of interstitial glass pigmented into brown with 

 very fine dusty inclusions. The felsic and mafic components are 

 nearly equal in quantity and the texture is granular intersertal or 

 typically basaltic. 



3) Two-pyroxene-basaltic bandaite. (The third type of the 

 somma lava.) (PI. II. Figs. 2-3.) 



The rock of this type is marked by the presence in moderate 



