832 DIAMOND-DEPOSITS OF COPETON, N.S.W., 



clear, hexagonal crystal, in the darker mass surrounding it, is a 

 quartz-crystal in chlorite. This structure occurs only on a small 

 scale, but it is very characteristic of the whole rock. In places, 

 the quartz has been partly resorbed, and the chlorite-fibres 

 penetrate into it. Again, it is not uncommon to find a modified 

 graphic intergrowth of chlorite and quartz. From this, it would 

 seem that the quartz crystallised rather before the chlorite, on 

 the whole, but that, in certain parts, the crystallisation was 

 simultaneous. 



These relations of the quartz and chlorite seem opposed to the 

 derivation of these minerals from a primary mineral, such as 

 hornblende or augite, or even from a glassy base. On the other 

 hand, much of the magnetite and ilmenite appears to be of a 

 secondary nature. The opaque crystals are, in places, moulded 

 about the felspars and the augite. A considerable amount of 

 the iron-ores appears to be associated with the chloritic material. 



A number of acicular crystals are present, which are idio- 

 morphic to the felspar. These appear to be tremolite. They do 

 not appear to bear any definite relation to the chloritic material. 



Leucoxene is present, bordering the ilmenite. 



Quartz-dolerite. /,oc.— Staggy Creek. 



Crystallinity : holocrystalline. 



Grainsize : relatively evengrained, the normal crystals varying 

 from 2 to 5 mm. in diameter. 



Fabric : a network of plagioclase felspars, with grains of nearly 

 colourless augite. The augite is very subordinate in amount, 

 being distinctly less abundant than in the Oakey Creek dolerite. 

 There also occurs a considerable amount of interstitial chlorite, 

 as in the Oakey Creek dolerite. 



The chief minerals, in descending order of abundance, are 

 oligoclase, labradorite, augite, chlorite, ilmenite, magnetite, 

 quartz, and biotite. 



The felspars are very similar to those of the Oakey Creek 

 dolerite, but the sample was not so fresh in this rock, and the 

 felspars, consequently, are more kaolinised. The most basic 

 felspar observed was labradorite of the composition AbgAn-, and, 

 the most acid, an albite-oligoclase. Zoning occurs in the felspars, 



