796 GENERAL GEOLOGY OF MARULAN AND TALLONG, N.S.W., 



always in parallel position, with the pyroxene inside and the 

 hornblende peripheral in position. The diopside is colourless, 

 much twinned in broad lamellae, and shows extinction-angles up 

 to 45'^ from the trace of the vertical axis. It is almost all more 

 or less altered to uralite, all stages from incipient alteration to 

 <3omplete replacement by a finely fibrous aggregate of light green 

 uralite being noticeable. 



Hypersthene occurs, like diopside, intergrown with hornblende, 

 but no instances have been seen of intergrowth of the two pyrox- 

 enes. It is very slightly coloured, and shows very faint pieo- 

 chroism in pink and yellowish tints. Like the diopside, it is 

 considerably altered, but not to uralite. It gives rise to a cloudy, 

 brown, fibrous aggregate of bastite, with straight extinction 

 between crossed nicols. 



In addition to the intergrowth with pyroxene, hornblende 

 forms subidiomorphic crystals up to 2 mm. in length. Its optical 

 properties call for no particular description. 



Biotite is somewhat irregular in occurrence, being met with in 

 considerable abundance in some parts of a slide and very scarce 

 in the remainder. It occurs in idiomorphic and subidiomorphic 

 grains uptoO-75mm. by0-5mm.; pleochroism from bright yellow 

 to very dark red-brown. It is somewhat decomposed round the 

 edges and along the cleavages into green pleochroic chlorite 

 (pennine). There are also narrow lenses of colourless mineral 

 ^talc ?) along the cleavages. 



Magnetite is fairly abundant in large irregular grains up to 

 0-5 mm. in diameter. A few sharply defined, but minute, crystals 

 of zircon and apatite occur. Order of consolidation — 



Zircon and apatite 



Magnetite 



Plagioclase 



Biotite 



Hypersthene and diopside 



Hornblende — — - 



Orthoclase and quartz 



