GEOLOGICAL OBSKHVATIONS LV FIJI. 133 



augite and feldspar may be seen under the microscope, but the ground- 

 mass forms, on an average, 90 per cent of the rock. The feldspars 

 forming the ground-mass are larger than usual and show a flow arrange- 

 ment with small, roimded augites in the interstices. The feldspar 

 has the composition of a basic andesine or acid labradorite, Abs^Auis- 



The texture of the ground-mass is exceptional for Fijian lavas and 

 may be called trachytoid. 



2) Hornblende Andesite. Hornblende andesites of practically the 

 same composition are very widespread in Kandavu. They have been 

 described by Wichmann (1882, p. 32) from the island of Ono, by 

 Eakle (1899, p. 586) from Mount Washington, a very recent cone, 

 and by Renard (1888, p. 149) from Vunisea. The specimens collected 

 by the writer, were found at Vunisea, Joma and Namata. A typical 

 specimen from Namara will be described. 



The fresh andesite is bluish gray in color, hypocrystalline, and 

 porphyritic. There are abundant phenocrysts of feldspar, 10 to 

 12 mm. long and 4 to 6 mm. wide; large hornblende needles, 5 to 

 6 mm. long, are also plentiful. Euhedral phenocrysts of diallagic 

 augite are also present. 



The hornblende has an opaque reaction rim about it, such as Renard 

 (1888, p. 151) described as consisting of magnetite and secondary 

 diopside. Though the hornblende has changed to diopside within 

 its mass, the larger part of the reaction rim appears to consist of 

 magnetite. The hornblende is a basaltic, pleochroic variety; yellow 

 // X, darker yellow // Y, and olive yellow to brown // Tj. 



Analysis gave the following result: 



Norm 



SiOo 59.70 



TiO., 0.45 Quartz 7.80 



\l2O3 16 . 59 Orthoclase 14 . 46 



Fek)3 . . . . . '. . . . . . . . . . . . 1 . 70 Albite 34.06 



PeO 3 . 56 Anorthite 20 . 02 



MnO 0.05 Diopside 8.06 



]\IgO 4 . 18 Hypersthene 11 . 10 



CaO 6.18 Ilmenite 91 



NaoO 3.97 Magnetite 2.55 



K2O 2 .37 Apatite -31 



H2O 1.10 99.27 



P0O5 0.22 Water 1.10 



100.07 100.37 



