GEOLOGY AND PETROLOGY OF ENOGGERA GRANITE. 137 



these large hornblende crystals, showing clearly that at 

 least the latter part of the growth of the hornblendes was 

 subsequent to the consolidation of the plagioclases. This is, 

 of course, seen best in prismatic sections of the hornblende, 

 transverse sections often showing beautifully idiomorphic 

 outlines with both sets of cleavages well developed. The 

 mineral is light-green in colour, strongly pleochroic, and 

 shows alteration to Chlorite. Biotite is very rare, but those 

 few small crystals present are definitely idiomorphic to the 

 hornblende. Augite is present in three very small crystals. 

 Magnetite is present in considerable amount, but is largely 

 pseudomorphous after Pyrites. Sphene and xipatite are 

 present, but in very small amount. 



Order of consolidation . — Biotite, Andesine, Horn- 

 blende, Orthoclase, Quartz. 



Name. — Hornblende Quartz Diorite. 



{G.41) 345. — Specimen from near "The Summit," Taylor 

 Kange. 



This forms a connecting link between the more typical 

 hornblendic rock (G. 44) on the one hand and the biotitic 

 rock (G. 14) on the other. 



Megascopie.^A grey holocrystalline fine-grained rock, 

 made up for the most part of white plagioclase and dark 

 hornblende, together with very small flakes of biotite and 

 numerous small crystals of pyrites. 



Microseopie. — Holocrystalline, fine-grained. Q uartz 

 occurs as interstital growths, which (since the other 

 minerals are strongly idiomorphic) are bounded by 

 numerous short straight lines running at various angles, 

 thus giving a curious graphic appearance to the mineral. 

 Other somewhat larger plates are seen enclosing smaller 

 crystals of all the other minerals. OrtJiocIase occurs as a 

 few comparatively large, irregular crystals (up to 3 mm.), 

 idiomorphic only to the quartz and showing perthitic inter- 

 growths with another felspar. Plagioclase is present as 

 numerous, mostly small, idiomorphic crystals, showing fine 

 Albite twinning, but with a zonal extinction pointing to a 

 considerable variation in chemical composition in each 

 individual. In addition to these felspars is a large 

 irregularly rounded crystal of plagioclase. The round outer 



