260 W. R. BROWNE AND W. A. GREIG. 
ON AN OLIVINH-BEARING QUARTZ-MONZONITE 
FROM KIANDRA, N.S.W. 
By W. R. BROWNE, D.Sc., and W. A. GREIG. 
With Plate XIV. 
{Read before the Royal Society of N.S. Wales, December 6, 1922. 
Introduction. 
~The association of olivine and primary quartz in an 
igneous rock is a comparatively rare phenomenon. Apart 
from the occurrence of the iron-olivine, fayalite, in cavities 
in rhyolites, olivine in rocks other than basic appears to be 
confined mainly to lavas and quickly-cooled intrusions. 
Theoretically olivine is unstable in the presence of free 
silica, the tendency being for the orthosilicate to take up 
sufficient silica to convert it into the metasilicate, enstatite 
or hypersthene. Hence the association of olivine and free 
quartz, even in small amounts, in a plutonic rock is of 
interest, and this circumstance, coupled with the fact that 
so far as we are aware, the rock under consideration is only 
the second monzonitic type yet described from this State, 
will perhaps serve as some justification for the detailed 
nature of this communication. 
The rock in question outcrops at Pollock’s Gully, in the 
township of Kiandra, on the Southern Tableland of New 
South Wales. It is briefly mentioned by Mr. H.C. Andrews, 
B.A., in his report on the Kiandra Lead, under the name of 
norite,* and indeed the ‘specimens which have been inves- 
tigated by us were probably collected by Mr. Andrews. 
They have been made available through the courtesy of the 
Ourator of the Mining Museum, Mr. G. W. Card, A.R.S.M. 


1 N.S.W. Depart. of Mines, Mineral Resources, No. 10, 1901, p. 17. 

