THE GEOLOGY OF MITTAGONG. aa. 
Olivine occurs in comparatively large masses, usually of 
irregularly circular shape, but prisms and hexagonal cross 
sections are fairly numerous. The olivine has not undergone 
serpentinisation, and is therefore clear and colourless with 
well defined edges. The remaining minerals are much 
smaller and of the ordinary types occurring in basalts. 
Order of Consolidation. 
Olivine | 
om fr felspar 
magnetite 
augite 
glass 
Name.—From the abundance and size of the olivine 
crystals the rock may be termed an OLIVINE BASALT. 
No. 8. Locality McGuire’s Creek, 7 miles east of 
Mittagong. 
Texture—Hypocrystalline with large phenocrysts. 
Fabric—Dense dark base consisting apparently of small 
grains of magnetite in a glassy paste. Small ragged 
laths of plagioclase and irregular masses of magnetite 
together with some olivine are scattered through the 
base. Large phenocrysts of felspar and olivine are 
noteworthy. The flow of the small felspars round 
these large crystals is well shown. 
Minerals present (in order of decreasing abundance)— 
Magnetite ba ee tes a Prieto Uy 
Felspar (of two orders) >» aa poe aE 
Olivine (of two orders) a3 ay aosimeOre 
Plagioclase.—The small felspars are of usual lath shape 
and show twinning carlsbad and albite law, probably of 
variety labradorite. The phenocrysts are in some cases 
idiomorphic, while in others the edges are rounded and 
corroded. They are asarule broader in proportion than 
the small felspars. The albite law of twinning is followed. 
