THE METAMORPHIC ROCKS OF ADEL1E LAND. 8TILLWELL. 85 



The quartz is present in irregular, indented grains, and frequently shows marked 

 cataclasis. Some of the original crystals are replaced by interlocking granular aggregates 

 with undulose extinction. Well marked strings of linear inclusions frequently pass 

 through adjacent grains in such aggregates. Microcline, with its characteristic cross 

 hatching, is abundant, and has developed from the original orthoclase of the granite. 

 In some cases the transition from orthoclase is incomplete, and clear orthoclase forms 

 the bulk of the crystal, which possesses a fringe with the cross twinning of microcline. 

 The microcline exhibits some cataclasis. Perthite or networks of soda plagioclase 

 and orthoclase are common in large individuals. The orthoclase is in large plates, 

 and an albitic plagioclase appears in short, broken, more or less parallel strings which 

 have the higher refractive index. This perthitic intergrowth can be found along lines 

 of incipient fracture. Diablastic intergrowths of quartz and felspar, or of orthoclase 

 and plagioclase, similar to the micropegmatitic intergrowths, are common. It is 

 evident that the intergrowth has a metamorphic origin, because, not only are they 

 most frequent in the crush areas, but they may be seen, with a rounded outline, 

 developing parasitically within a plagioclase crystal. Sericite has developed from the 

 orthoclase and is chiefly to be found in the crush areas. Like secondary biotite, it tends 

 to wrap itself around primary quartz and felspar. In one case it appears as a zone 

 between two microcline crystals. It may also appear as a rim on biotite crystals 

 bending with the biotite. The original plagioclase has a refractive index above basal 

 quartz and below other grains of quartz, and is, therefore, referred to as andesine. The 

 application of Becke's bright line method is limited because the edges of the crystals 

 are frequently crushed. Saussuritic aggregates have, in some cases, developed from the 

 andesine, but only granular epidote and rounded blebs of secondary felspar can be 

 distinguished in them. 



Biotite is common in the crush areas but it is not confined to them, and some of it 

 may have been preserved from the original granite. In some cases it tends to wrap 

 itself around the relic quartz and felspar. Its colour is normally brown, but there 

 is a subordinate quantity of green. Green chlorite in small amount is interlaminated 

 with biotite. The biotite is often associated with epidote, sphene, and magnetite. 

 Sometimes there is a thin rim of granular epidote around the biotite. The rim may 

 also be sericite, which may develop into muscovite, because the latter is sometimes 

 associated with the biotite. Muscovite is sparingly present in individuals comparable 

 in size with the biotite. Pleochroic halos in biotite appear around inclusions of zircon 

 and sphene. Epidote is present either in pleochroic crystals and grains or in the finely 

 granular form. It is frequently associated with the biotite. 



Sphene is usually granular, but some wedge-shaped crystals are seen. Sometimes 

 it encloses a magnetite core, but not so frequently as in the amphibolites. Both sphene 

 and epidote may be completely enclosed in biotite. Granular calcite has been found 

 and has probably developed with the saussurite. Apatite, zircon, pyrite, and magnetite 

 are scattered throughout. The apatite may be in large crystals, and the zircon is 

 noticeable in small well-defined crystals with pointed ends which have clearly never 

 left their primary host. 



