CORDIERITE BEARING-ROCK FROM BROKEN HILL. 217 
Veins of pegmatite occur not far distant, and the rocks generally 
in the neighbourhood are the highly metamorphic schists and 
gneisses, with intercalated amphibolites,' typical of this portion of 
the Barrier Ranges. Rocks of a granulitic type—both acid and 
basic—have been pretty extensively developed around Broken 
Hill, but garnet-granulite is the one most commonly met with, 
and cordierite-granulite the rarest, but it is quite possible that, 
unless the cordierite is in large crystals in the rock, the cordierite 
rock is not so often noticed as the garnetiferous variety is. 
Cordierite may be found forming the centre of the felspar 
“augen” of an augen-gneiss, close to its junction with a basic 
eruptive rock, at a locality about three miles and a half to the 
east of Block 14 Mine. In that case the resemblance of the 
felspar knots to “eyes” is most. strikingly accentuated by the 
cordierite forming, as it were the dark “ pupils.” 
Petrographical Description.—I have prepared several sections 
of the granulite under discussion, for microscopical examination. 
ome of them were taken hap-hazard from flakes struck off with 
a hammer, others were cut, with a lapidary’s slitting-dise of soft 
iron charged with splinters of diamond, so as to include crystals 
of cordierite recognisable as such in hand specimen. The rock is 
a perfectly compact holocrystalline-granular one, in which the 
minerals are allotriomorphic. Its texture is, on the whole, rather 
fine, almost saccharoidal in parts. Its strong coherence admits 
of the production of large and thin sections with ease. 
The component minerals are as follows :— 
Felspars—(a.) Orthoclase is fairly abundant throught the rock. 
Microcline (herewith included) is likewise abundant, and these 
two are the predominating felspars. The orthoclase is fairly 
fresh, and shows the common twinning on the Carlsbad type. 
The microcline shows the peculiar “ cross-hatching ” between 
crossed nicols, due to multiple twinning. In some cases, however, 
it presents only a series of twin lamelle of peated dimensions. 
eee. see ore 
md B. Jacquet, op. ‘Git. 
