114 M. A. Farquharson — Petrology of N. Kalgoorlie. 



that the felspar is albite or albite-oligoclase. The ground-raass 

 consists of innumerable fine laths of twinned felspar with, in places, 

 an approach to felted structure, a fact which tends to show that the 

 rock consolidated sensibly under atmospheric pressure conditions. 

 Quartz occurs not only in minute plates, but also in mosaic aggregates 

 and in one or two rather large forms, which are, however, quite 

 without definite outline. In some places the felspar phenocrysts 

 present corroded margins as if the ground-mass had reacted on the 

 phenocrysts. In other cases they appear to be partially replaced by 

 clear quartz and muscovite. 



To settle all doubt as to the nature of the predominant mineral 

 a chemical analysis of the rock was made in the Survey laboratory, 

 with this result — 



78-80 



Total 



100-31 



The absence of Kg and the high percentage of Nag with the low 

 percentage of CaO show conclusively that the species is highly 

 sodic, and mostly, if not wholly, albite. Moreover, the high silica 

 percentage bears out the identification of quartz in the ground-mass. 



This analysis was compared with those of some rocks of other 

 localities : — 



Total . 100-28 100-44 100-21 99-83 100-31^ 



1 Quartz-keratophyre (Eosenbusch, Gesteinslehre, 1910, p. 329). 



2. ' 



3. Quartz-diorite-porphyrite (Osann, Beitrage sur cJieviischen Petrographie, 



p. 87). 



4. Keratophyre (brown), Osann, p. 120. 



5. Analysis of 12331A re-quoted for comparison. 



Gliiliverlust. 



{To be continued.) 



^ Includes C O2, Fe S2, and H2 0. 



