Volcixr.o Oshinia. Lizii. 91 



Olivine plionocrysts, next to those of anorthite in amount but 

 far less numerous, range in diameter from 0.3 to 1 mni. Theso 

 have irregular outlines with rounded corners and sometimes deep 

 indentations, each being fringed witli a resorption -border, consisting 

 of magnetite grains, surrounded in turn by a specially fine- 

 grained thin layer similar in composition to the groundmass. The 

 refractive indices of olivine crystals were measured witli the 

 result: «< 1.678 </3<l.G91<r. The mineral is therefore inferred 

 to have the chemical composition (Fe2Si04)i-i_i9(Mg.^Si04)87-si. The 

 mineral is fresh, but irregularly cracked, and is almost free from 

 inclusions except fluid enclosures which are very rarely found. 



Subordinate phenocrysts of hypersthene and augite are present. 

 Hypersthene phenocrysts are subhedral and prismatic, the largest 

 in thin section measuring 1 mm. along the c-axis, and are traversed 

 by the usual cleavage lines and other cracks, of which those 

 perpendicular to the c-axis are conspicuous. The mineral has the 

 optical plane parallel to (010) and shows its characteristic pleo- 

 chroism. As inclusions it often contains small plagioclase crystals. 



Light greenish augite phenocrysts, 0.8 mm. across in the 

 largest example are eujiedral to anhedral, twinned sometimes on 

 (100). 



A parallel growth of two pyroxenes is commonly seen, the 

 hypersthene being always enclosed by a very thin rim of augite. 



Tlie minerals in the groundmass are prismoid plagioclase which 

 is at least as calcic as labradorite-bytownite with the maximum 

 symmetrical extinction angle reaching 45^, light greenish anliedral 

 augite, and euhedral isometric magnetite, with an extremely small 

 amount of interstitial glass, light brown in colour, clouded by 

 numerous globules. These component minerals vary from 0.01 to 

 0.1 Dun. in diameter and build up the granular intersertal ground- 



