34 AUSTRALASIAN ANTARCTIC BXPEDITION. 



curved against the chlorite. Granular epidote is present and can be distinguished from 

 the lawsonite by its colour and pleochroism. Sphene is a moderately abundant accessory. 

 The rock is the best example obtained in situ of a lawsonite amphibolite. 



No. 630. This sample comes from one of the thicker outcrops. The outcrop is 

 remarkable in containing a patch of rock which appears to be mostly biotite in the hand 

 specimen. The difference noticed underfoot in passing from the ordinary rock to the 

 biotite is similar to the difference between a pavement and a carpet. The hand 

 specimen is, perhaps, not so dark coloured as the other examples. The measured 

 section is cut at right angles to the plane of schistosity but not at right angles to 

 the direction of stretching. This, however, has not affected the general character of the 

 individual. 



The mineral composition shows an extraordinary percentage of the colourless 

 components, felspar and quartz, but examination shows that there is much more quartz 

 than usual. The quartz is occasionally in large grains, clear, and often without wavy 

 extinction, and so grouped as to suggest segregation or absorption of secondary silica 

 into the rock. This quartz gives the rock an abnormal silica percentage. The clear 

 felspar is about equal in amount to the saussuritised felspar, but their distribution is 

 quite irregular. Clear felspar is dominant in some parts of the slide and saussuritised 

 felspar in other parts. Some comparatively clear felspar with broad lamellae can be 

 found. Extinction angles up to 37 can be measured, and labradorite is therefore 

 present. Sometimes the calcic plagioclase is partly saussuritised, and the saussuritisa- 

 tion is more intense along one alternate set of lamellae. Such examples suggest that 

 it is a relic felspar. Apart from this calcic plagioclase is another plagioclase, always 

 in clear rounded interlocking grain, which is interpreted as an oligoclase or andesine. 

 The biotite is curious. Some biotites are pleochroic in cross sections from a light-straw 

 colour to a dark brown, while other biotite crystals are pleochroic from a pale-greenish 

 yellow to a deep-emerald green. That there is no great difference between the brown 

 and green varieties is shown by the way the brown and green may be laminated in one 

 and the same crystal. The polarisation colours of the green part are too high for green 

 chlorite. In some parts, when in association with the cloudy felspar, the green mica 

 is a little paler and more like chlorite. Here lenticles showing the ultra blue polarisation 

 colour may be found. Epidote is associated with the green biotite in the same way 

 as it is associated with chlorite in No. 5. It seems that we have here the change from 

 chlorite to biotite during the process of recrystallisation. The chlorite passes over 

 into biotite with the absorption of alkali first by deepening its green colour and later 

 by changing colour to brown. The hornblende is normal. Epidote, sphene, and apatite 

 are relatively abundant. Occasionally the grains of epidote are found with a nucleus 

 of calcite and magnetite. The calcite has been formed from the decomposition of a 

 primary mineral, and at this centre of recrystallisation there has been more calcium 

 and iron available than actually necessary for the production of epidote. Epidote 

 sometimes forms a pale border to a red-brown mineral, pleochroic with high refractive 



