150 R. A. Farquharson — Petrology of N. Kalgoorlie, 



qaartz, granular patches of an iron-stained carbonate, some grains 

 of magnetite, and a few patches of green scaly chlorite. One or two 

 larger plates of quartz are to be observed, but phenocrysts of the 

 mineral are conspicuously absent. The species of felspar present was 

 indeterminable owing to the alteration the mineral has undergone. 



The rock may be either a quartz-porphyry, with quartz wanting 

 among the phenocrysts, or an altered specimen of keratophyre. 



[h) The Non-Porphyritic Type. 



12231. In hand-specimens, the same in appearance as the other 

 brown specimens. In section the rock is seen to be devoid of felspar 

 phenocrysts, and to consist of a plexus of trimmed laths of felspar, 

 among which quartz is very hard to identify. In the ground-mass 

 are several long, thin, acicular as well as rectangular crystals, yellow 

 in colour, which are doubtless chloritized remains of hornblende forms. 

 Here and there are pieces of tourmaline without definite shape, with 

 a dichroism from deep green to pale violet or lavender. 



12233 is in a hand-specimen a light-grey, compact, fine-grained 

 rock with a brown crust. The section is composed entirely of 

 irregularly outlined laths of felspar of considerable size, some 

 interstitial quartz, and some aggregates and scattered scales of 

 greenish pleochroic chlorite with grains and squares of magnetite. 

 Phenocrysts are absent, though some of the laths attain unusual size 

 (PI. VII, Fig. 3). Twinning is pronounced, and measurements of 

 extinction angles indicate albite or oligoclase-albite. The irregular 

 nature of the outline of the laths is a noteworthy feature. 



B. EocKS OF Gabbroid or Doleritic Origin. 



The rocks of this group are either light-grey with green spots and 

 rather hard, e.g. 12324, or dark-gieen, soft, and with minute quartz 

 crystals, e.g. 12379. As stated previously, the distinctive characters 

 of the group are few, but generally there are clear outlines of long 

 columnar twinned felspars, and in two specimens at least, 12324 and 

 12^22, a kind of coarse ophitic structure. 



12324. Minerals observed : hornblende, felspar, quartz, zoisite, 

 epidote, chlorite, apatite, iron-oi"e. 



The section consists of large ragged plates and flakes, of a pale, 

 almost colourless hornblende that is sometimes partially chloritized, 

 disposed amongst numerous completely turbid rectangular and 

 columnar crystals of felspar, with idiomorphic outline. The turbidity 

 is seen with high powers to be due to a granular mass of zoisite, 

 epidote, and occasionally clear quartz, and is consequently to be 

 attributed to saussuritization. Between the felspar crystals there 

 is frequently some clear interstitial quartz that is, without doubt, 

 original. Long needles of apatite occasionally make their appearance, 

 and besides forms of lnucoxene there are grains of ilmenite 

 surrounded by that mineral. 



The idiomorphic nature of the felspars and the platy character 

 of the hornblende suggest a sub-ophitic structure. The rock is an 

 amphibolized and partially sa*ussuritized quartz dolerite. 



12322 differs from 12324 only in a greater development of felspar 

 forms, and a smaller development of the ferro-magnesian and quartz. 



