54 
Geology of Sydney 
The following tabular statement 
mineral from quartz, 
may prove a help. 
QUARTZ 
is very hard ; 
it easily scratches glass ; 
is not scratched by a knife ; 
shows on breaking no flat and 
lustrous faces , due to cleav- 
age; 
is infusible ; 1 
is insoluble ; 
does not easily decompose ; 
is glassy looking ; 
breaks with rounded faces; 
is usually transparent ; 
has a non-metallic lustre. 
FELSPAR 
is not so hard as quarts ; 
does not easily scratch glass; 
is barely scratched by a knife ; 
on breaking shows flat and 
lustrous faces, due to cleav- 
age; 
fuses with difficulty ; 
decomposes into Kaolin ; 
has rather a pearly than 
glassy look ; 
breaks with flat faces ; 
is translucent, but usually 
somewhat turbid ; 
has a non-metallic lustre. 
5. AUGITE. — Augite is not far removed from Horn- 
blende. It is a very abundant and important 
rock-forming mineral. In color it is green to 
black, and although an essential constituent of 
Basalt, is not often visible to the unaided eye. 
In some basaltic districts, crystals of augite are 
found amongst the decomposed rock material in 
short prisms. 
As Mica is the third constituent of Granite, and 
Hornblende is also a constituent of most Australian 
1 Infusible in an ordinary blowpipe flame without any flux. With carbonate of 
soda as a flux, quartz fuses before the blowpipe 
