14:0 PROCEEDINGS OF THE ROYAL SOCIETY OF QUEENSLAND, 



(c) The (?) Hybrid Rock. 

 This occurs as a patch a few acres in extent on the 

 left bank of Enoggera Creek and about one-third of a mile 

 from the eastern edge of the granitic mass. It is entirely 

 surrounded by rocks typical of the Pink Phase. This rock 

 has been quarried and used to some extent in public build- 

 ings in Brisbane and for kerbing purposes. It is known 

 commercially as the "P]noggera Granite." (See analysis 

 E. 2 and mierophotograph Plate III., No. 7.) 



(G. 6) 154. — From the Quarry, Enoggera Creek. 



Megascopic. — In the hand specimen the preponderance 

 of the light-coloured "salic" minerals over the dark- 

 coloured "femic" minerals and the small size of 

 individuals, and especially those of the latter group, give 

 to the rock a somewhat curious "pepper and salt 

 appearance,"^" and a general absence of relief. 



Microscopic. — Holocrystalline, medium-grained, the 

 grain size, however, being somewhat variable, the resulting- 

 texture resembling the "seriate porphyroid fabric" of 

 Iddings. Quartz occurs as allotriomorphic crystals from 

 1-3 mm. in diameter, fresh, generally unbroken, enclosing 

 numerous large crystals of felspar. It also occurs commonly 

 with orthoclase in micrographic intergrowths. Orthoclase 

 occurs as hypidiomorphic crystals of varying size, some- 

 times as inclusions in quartz and sometimes in micro- 

 graphic intergrowths. Carlsbad twinning is seen and 

 inclusions of another felspar tend to give a rudely perthitic 

 structure. It is usually considerably darkened and altered.. 

 The Plagioclases present are mostly intermediate andesine. 

 A few crystals of oligoclase-andesine are present, and in 

 addition there are a number of zoned plagioclases. Albite 

 twinning is common, and Pericline twinning combined with 

 Albite is not infrequent. All these felspars are darkened 

 as a result of decomposition, and while some crystals are 

 hypidiomorphic, the majority of them, and particularly 

 the more basic, show irregular embayed and corroded out- 

 lines. Biotite occurs as rather small brown and green 

 crystals, sometimes considerably bleached and altered into 

 chloritic material and usually strongly pleochroic. Horn- 

 blende occurs very sparingly as green idiomorphic pleo- 

 chroic crystals. Pyrites occurs commonly, generally in 



"H. C. Eichards, Op. cit. p. 102. 



