BY THE BRITISH ANTARCTIC EXPEDITION, 1007 1909 



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lepidoblastic structure owing to the biotite occurring in flakes, but the distribution of 

 the flake does not point to any foliation in the rock. 



The constituent minerals are : quartz, felspar, biotite, pyroxene, sphene, magnetite, 

 and apatite. 



Quartz is easily the most abundant mineral. It is in allotriomorphic grains, and 

 shadowy extinctions are very prominent. It does not appear to be granulated to any 

 extent. ' The felspar is not very abundant and is mostly untwinned. It is quite fresh 

 but has numerous minute inclusions. Biotite is fairly plentiful in small ragged, elongated 

 flakes, and gives the rock a somewhat lepidoblastic appearance. In some cases it is 

 decomposing, the brown colour being altered to green and the D.R. slightly decreased, 

 thus showing change to chlorite. Pyroxene is present in colourless allotriomorphic 

 bunches. It is diopside. Sphene is present in fair quantity. It is in small characteristic 

 sections, and these have a tendency to cluster together in bunches. Zircon, apatite, 

 and magnetite are sparingly present. For an analysis of this rock see p. 161. 



MINERALOGICAL COMPOSITION OF ROCKS 



