Geology and Petkology of Part of Toodyay District, W.A. 95 
coarse granoblastic structured types in which the amphibole occurs in pale 
greenish prisms with irregular terminations, either included in the quartz or 
set between cjuartz grains. It all has the same orientation and thus tends to 
give a banded appearance to the rock. Rarely, grossularite is noticed as 
a constituent of the felspathic quartzites (specimen 1248). Irregular shaped 
epidote granules and small lozenge shaped idioblasts of sphene are also in- 
cluded in the quartz. In these rocks the (Ca, Mg) silicates are only present as 
accessories. 
A. Quartz-diopside-epidote-grossularite rock (1249), showing 
grossularite aggregates, with associated sphene, epidote and 
diopside. The clear areas are quartz xenoblasts. 
B. Hornblende-diopside quartzite (15405) witli grossularite 
(at top) and carbonate (centre and bottom). 
An increase in the dolomitic impiirity in the original sediment leads to the 
<levelopment of several types of rock ; — - 
(a) Q.uartz-epidote-diopside-grossular rocks. 
(b) Hornblende-diopside quartzites. 
The former type {e.g., specimen 1249) is a fine-grained, massive, pale yellow^- 
ish, homfelsic rock with a banded structure, due to the presence of parallel 
seams and lenses of vitreous ciuartz, one or two mm. in length. Under the 
microscope the constituent minerals are : — grossularite, epidote, diopside, 
quartz, and sphene. 
The grossularite is the most abundant constituent forming 00 per cent 
or more of the rock. It occurs in aggregates of small idioblastic crystals of 
])ale yellow colour. The irregular interspaces are occupied by clear unstrained 
quartz, towards which the garnet is always idioblastic, also drop-like quartz 
imdusions are common in the garnet. The garnet is all isotropic and has 
N 1*70.5 (by immersion in oils) and is, therefore, a grossularite with slight 
admixture only of the other garnet molecules. 
A pale yellow coloured epidote with very weak pleochroism is fairly 
abundant, generally in skeletal crystals which, except for the development 
