10 B. Eotô : 



and granules of magnetite. Next in abundcnice is iron-ore, which 

 occurs in octahedra or clumps, periplierally changing into leu- 

 coxene (titano-magnetite). 



Nepheline is the characteristic ingredient occuri'ing in short 

 prisms, the basal section of which is hexagonal and the longitudinal 

 section rectangular. These colorless crystals (the largest being 

 0.13 by 0.11 mm.) occur in large quantities (30% of the volume) 

 and are fresh with a vitreous lustre ; tliey enclose rounded augite- 

 microlites arranged parallel to the contour of tlie host — a cliarac- 

 teristic habitus by Avhich the presence of nepheline can be easily 

 recognized. Through atmospheric decomposition the mineral 

 substance becomes parallel-fibrous by zeolitization along the 

 vertical axis, and in basal section the change is seen advancing 

 from the periphery. Low polarization-colors and other optical 

 behaviors are normal. With HCl and methylviolet the mineral is 

 easily ascertained by the staining method. 



Olivine. — The minutely porphyritic or minophyric phenocr^^sts 

 of olivine of variable size (usually less than 0.8 mm. by 0.5) occur 

 abundantly in euhedral or corroded subhedral shape, and occasion- 

 ally in glomeratic clusters. It often changes into a yellowish or 

 greenish fibrous substance, from which it may be inferred that it is 

 of a variety rich in magnesia. The olivine is colorless in section, 

 and encloses copious octahedra of hroirn spinel. Polarization- 

 colors are indigo-blue, purple, brown, and gray according to the 

 thickness and orientation of given sections. 



No sanidine or any other feldspars are pi-esent. Apatite is also 

 absent. Sporadic patches of a brownish basaltic base, granulated 

 and sometimes fibrous, fill up the interspaces left between the 

 idiomorphic nepheline'-*, and the overcrowded augite-microlites 



1) For example, around the hexagonal section of nepheline, PI. I. Jig. 2. 



