GEOLOGICAL OHSEUVATIONS IN FIJI. 101) 



The phenocrysts are olivine and lahradorite, Al)^o Aiico, with a few 

 augites. Augite, lahradorite, magnetite, and secondary minerals 

 compose the ground-mass, which has an ophitic structure. 



()) OUnnc Basalt from Lautoka. Masses of greenish-black olivine 

 basalt occur as residual boulders on the late-mature hills about Lau- 

 toka, on the western side of Viti Levu. 



The rock is holocrystalline and very fine-grained. The pheno- 

 crysts in the rock consist of stubby, euhedral augite (4 to 5 mm. long) 

 and romided grains of zoned plagioclase, AbosAnxs to AbrAngs, (2 to 

 3 mm. long) with many oli\ine crystals. 



The ophitic ground-mass is composed of olivine, augite, feldspar 

 and abundant minute flecks of magnetite. Serpentine is secondary 

 after the olivine. 



The following analysis shows that the basalt is quite basic in com- 

 position. 



Norm 



SiO. 47.36 



TiOo 85 Orthoclase 10.01 



AWs/^'^'^'^'.'.'.'.'.'.'.'. i9'38 Aibite 20.96 



FeoOs 3.60 Nephelite 1.14 



FeO 6.13 Anorthite 35 . 58 



MnO 0.11 Diopside 12.82 



Olivine 9 . 76 



CaO 10.54 Magnetite 5.34 



NaoO 2 . 69 Hmenite 1 . 67 



MgO 

 CaO. 

 NaoO 



K2O 1 . 74 Apatite .31 



H2O 2.20 97.59 



P2O5 0.19 Water 2.20 



100.10 99.79 



Specific gravity at 20°C = 2.855 



Its position in the norm classification is: — 



Class 11 Dosalane 



Order 5 Germanare 



Rang 3 Andase 



Subrang 4 Andose 



7) Olivine Basalt from Na Sana Sana. The basalt, here described, 

 occurs as a dike, 10 to 15 feet in width, in the elevated coralliferous 

 limestone near Na Sana Sana, southwestern coast of Viti Levu. 



