286 AUSTRALASIAN ANTARCTIC EXPEDITION. 



The structure of the rock is granoblastic and the texture is schistose. Magnetite 

 forms approximately one-third of the rock. Garnets have been fairly common but are 

 mostly altered. By far the greater part of the chlorite is derived from the biotite which 

 was originally very abundant. Epidote is present and quartz is common. In the 

 veins, the quartz shows brush polarisation and a larger grain size. Felspars are present 

 but they are so completely kaolinised that it is impossible to identify them. 



No. 55. This is a fine grained, dark, heavy crystalline rock of specific gravity 

 3-11. It possesses a strongly developed crystallisation schistosity. Glistening white 

 mica on the cleavage planes gives a lustrous appearance to the rock. Fragments of the 

 rock are strongly magnetic. 



The structure is both granoblastic and lepidoblastic. Magnetite is abundant 

 and ilmenite is also present as shown by the presence of white leucoxene. Hematite 

 occurs but the bulk of the 18-9 per cent, of iron ore is magnetite. Garnets are abundant, 

 the chief alteration being magnetite, though chlorite is also formed. A green variety 

 of biotite is very common and usually associated with muscovite, which appears to be 

 a later product than the biotite. The latter is much altered to chlorite. Quartz shows 

 strain polarisation and sometimes its recrystallisation has split flakes of biotite from 

 their parent crystals. Felspar is present but is largely kaolinised. It sometimes 

 exhibits the remnants of a fine twinning. Apatite is present. The rock is a Mica- 

 Magnetite-Schist. 



No. 889. This specimen possesses a moderate crystallisation schistosity. On 

 one side there is a well-developed shear face along which abundant ilmenite is developed. 

 In the mass of the rock, blue cordierite can be seen. 



Two sections were made of this rock, one of which was at right angles to the 

 schistosity. The magnetite percentage (26-9) was obtained from the latter section. 

 Intergrown with the magnetite, is a fair amount of hematite but ilmenite is not abundant 

 in the sections. The rock was originally rich in garnet which has been mostly altered 

 to a mass of quartz, magnetite, and either biotite or muscovite. Biotite is usually 

 accompanied by felspar and shows alteration to magnetite. Magnetite has also been 

 developed along a series of sub-parallel lines in the garnet (Plate II, fig. 3), and where 

 these meet, the alteration is complete. 



The biotite is a greenish-brown variety and contains numerous pleochroic halos. 

 Occasionally there is a slight development of chlorite from biotite but a much commoner 

 alteration has produced magnetite and muscovite. The last mineral appears to be 

 derived from either the garnet or the biotite. Cordierite is abundant in the section 

 cut at right angles to the schistosity. It is distinguished from quartz by faint pleochroic 

 spots and its pronounced signs of alteration. The bulk of the felspar is andesine but 

 some is more calcic, probably approaching labradorite. One fine example of a crystal 

 of andesine shows a graphic intergrowth with quartz. Apatite is abnormally biaxial 

 in its interference figure. The structure is heteroblastic and the rock is a Magnetite- 

 Garnet-Schist. 



