134 PROCEEDINGS OF THE ROYAL SOCIETY OP QUEENSLAND, 



often shows inclusions of plagioclase. biotite, and quartz. 

 The principal Plagioclase present is an albite-oligoclase, 

 but an acid andesine is also present; and further, a zonal 

 structure is sometimes seen. These felspars vary from 

 1-3 mm. in diameter and show Albite twinning commonly 

 and Pericline twinning occasionally. They contain as 

 inclusions crystals of biotite. Biotite occurs as brown and 

 light green crystals strongly pleochroic, with inclusions of 

 Apatite. 



Order of crystallisation. — Normal. 

 Name. — Biotite Granite. 



{G.26) 422. 



This is typical of the outcrop of the Pink Phase form- 

 ing the Green Hill area to the south of the main Enoggera 

 area. {See Microphotograph Plate II., No. 2.) 



Megascopic. — This is a holocrystalline, porphyritic 

 rock made up of phenocrysts of colourless quartz, white 

 felspar and black mica set in a fine-grained pink ground 

 mass. The rock is somewhat darker in appearance than 

 the specimens from the principal area described above, and 

 differs from them in the almost complete absence of pheno- 

 crysts of pink orthoclase. 



Microscopic. — Holocrystalline, porphyritic. The 



medium size cf the felspar phenocrj^sts, the fine-grained 

 ground mass and the general arrangement, including the 

 tendency of the felspar phenocrysts to form clusters, are 

 all characters in which this rock approaches very nearly 

 the rocks from the southern part of the main Enoggera 

 area. (Compare Nos. 1 and 2 of Plate I.) The ground 

 mass is made up of a microerystalline mosaic of quartz and 

 altered felspars, which, .judging by the pink colour of the 

 ground mass as seen in the hand specimen, are mostly 

 orthoclase. 



Quartz occurs as comparatively small rounded crystals 

 usually from -|-1 mm. in diameter. Further, this mineral 

 is not so abundant as in the specimens described above. 

 Orthoclase phenocrysts are rare. The Plagioclases present 

 are all strongly zoned, so that it is difficult to calculate 

 from them the proportion of lime to soda in this rock. 

 Biotite of the usual type is present. Magnetite and 

 Apatite are present in very small amount. 



