124 FOYE. 



Its position in the Norm classification is: — 



Class II Dosalane, 



Order 5 Germanare, 



Rang 3 Andase. 



Subrang 4 Andose. 



Yami Ycntu. 



1. Andesite. This rock forms dikes, 3 or 4 feet wide, cutting 

 ash beds, on the eastern side of the island. 



The rock is purplish brown in color. Phenocrysts of andesine, 

 AbeoAnss to Ab6oAn4o, in laths 3 to 4 mm. long, occur in a vitreous 

 ground-mass, bearing microcrysts of feldspar. 



2. Olivine Basalt. The island of Yanu Yanu rises in a cone, 270 

 feet high. Its main mass is made of the rock described below which 

 was collected from the summit of the island. 



The basalt is fresh, massive, nearly black, holocrystalline, and 

 medium to fine-grained. 



In thin section abundant small phenocrysts of olivine are seen with 

 other phenocrysts of augite and feldspar. The ophitic ground-mass 

 contains abundant augite, some olivine, considerable andesine, 

 Ab6oAn4o, and magnetite.. 



The analysis of the basalt is as follows : — 



Norm 



SiOo 48.56 



'Pi02 2 . 40 Quartz .78 



AI063 16.30 Orthoclase 3.89 



FeoOs 2.01 Albite. 17.29 



PpQ § Oj Anorthite. . 33.36 



MnO 0.10 Diopside 4.51 



MgO 8.76 Hyper.sthene 29.87 



(\^() 8.22 Magnetite ;>.02 



NaoO 2.04 Ilmenite 4.56 



K26 0. 70 Apatite .02 



HoO 1 60 97.90 



Fobs 0.30 Water 1 . 60 



99.63 99.50 



Specific gravity at 20°C = 2.889 



