290 AUSTRALASIAN ANTARCTIC EXPEDITION. 



inclusions. It shows strain polarisation and is at times difficult to distinguish from 

 cordierite; the latter is usually recognised by the pleochroic brown spots. Such 

 extinction angles as can be measured for the felspars are high, and these, in conjunction 

 with a high refractory index, suggest labradorite. Though most of the felspar is 

 clouded, there is occasionally a clear fresh felspar with an extinction angle of 10 degrees 

 and a low refractive index which is probably albite. No sillimanite is present. The 

 structure of the rock is granoblastic and the specimen may be called a Magnetite-Garnet- 

 Gneiss. 



No. 814. This is a banded type in which the bands are narrower at the centre of 

 the specimen than at either end. They are composed of quartz, garnet, biotite, felspar, 

 and magnetite, and the pink colour of certain bands is due to a predominance of garnet. 



Magnetite with a little intergrown hematite forms 14-7 per cent, of the section. 

 No ilmenite occurs and no reaction was obtained for titanium. The magnetite frequently 

 contains inclusions of quartz, biotite, and garnet and there is sometimes a rim of 

 magnetite around a garnet crystal, while cracks in the garnets may be filled with 

 magnetite. Garnet, which was one of the first minerals to be formed, has an average 

 grain size of about 0-25 mm., forming 12-6 per cent, of the section. Quartz and 

 felspar constitute nearly two-thirds of the rock. Quartz shows strain polarisation and 

 is relatively clear with respect to the felspar ; it frequently contains inclusions of apatite, 

 zircon, and garnets. The felspar is only slightly altered and ranges from andesine to 

 labradorite. A little orthoclase is present. The felspar contains inclusions of quartz, 

 magnetite, and apatite. The biotite is a brown variety with numerous inclusions of 

 garnet, apatite, and sometimes magnetite. The structure is granoblastic and the rock 

 is a Magnetite-Garnet-Gneiss. 



No. 245. This is a dark schistose type in which magnetite, garnet, biotite, and 

 quartz can be identified macroscopically. 



Magnetite is an important constituent of the rock and a fair amount of ilmenite 

 is intergrown with it. Chemical tests on this and the following specimen (No. 288) 

 indicates the presence of titanium. Magnetite crystals enclose quartz, biotite, and garnet. 

 Garnets (15-6 per cent.) are almost as numerous as magnetite (17-9 per cent.) and are 

 more idioblastic though they are smaller in size (0-14 mm.) Some have been altered to 

 quartz and micaceous products and others have produced epidote, as in No. 989. 

 Quartz and felspar are abundant. Numerous minute gaseous inclusions in the quartz 

 have a roughly parallel arrangement, but there are other small reddish inclusions which 

 are possibly hematite or rutile. Both orthoclase and plagioclase are present ; the 

 latter is mostly andesine but some approaches labradorite in composition. Microcline 

 with its typical cross-hatching is observed and the felspar is generally free from 

 alteration. Green biotite forms 9-2 per cent, and shows pleochroic halos around minute 

 zircons. Apatite and epidote are noted. The rock is a Magnetite-Garnet-Schist. 



No. 288. This rock is very similar to No. 245 in the hand specimen except 

 that it contains some moderately large porphyroblasts of magnetite. 



