THE GEOLOGY OF MITTAGONG. 335 
was consolidating. The mineral is opaque with metallic 
lustre—by incident light of an iron-black tint. Almost all 
sections show partial decomposition into white opaque 
granular leucoxene. The latter occurs along cleavage 
cracks and is very well shown in one or two basal sections. 
Many ilmenite crystals contain parallel-sided apertures. 
Augite occurs in irregular masses, which have filled in 
the spaces left by the felspar and ilmenite—though a few 
augites have a fairly regular hexagonal shape. It is sensibly 
ophitic, in many cases extinguishing simultaneously over 
comparatively large areas. The colour by transmitted 
light is pinkish-brown. None of the crystals are twinned. 
The augites are traversed by cracks along which incipient 
decomposition is taking place. Inclusions of apatite 
ilmenite and felspar are to be seen, due as stated above, to 
the later solidification of the augite. 
The felspars occur inv prisms, usually short and wide. 
Very few are polysynthetically twinned, the crystals being 
mainly untwinned or singly twinned. This fact and also 
the low refractive index (lower than Oanada balsam in 
many crystals) points to a preponderance of monoclinic 
felspar. The felspars are decomposed into kaolin and 
replaced by brown chloritic material especially round the 
edges of the prisms. Many crystals include an isotropic 
glassy material of refractive index less than that of the 
felspars. This mineral is probably analcime which not 
infrequently occurs in such a manner. 
The serpentine, together with the calcite and chalcedony 
present in the rock, may represent decomposed augite. 
The beautiful radiating tufts of serpentine show black 
crosses of aggregate polarisation. 
The calcite can be distinguished by its pale neutral tints 
under crossed nicolls, and by the rhombohedral cleavage. 
