Geology and Petrology of Part of Toodyay District, W.A. 105 
The less abundant microcline is all water-clear and shows the character- 
istic cross hatched twinning. Microcline although rarely present in amounts 
exceeding 5 per cent is a constant constituent of these rocks. 
The only accessory is sphene, in small imperfect crystals usually en- 
closed by hornblende. 
This rock has been analysed as typical of these hornblende schists (Table 
1, col. 1). It is an analysis closely resembling that of igneous rocks of the 
composition of quartz dolerite. An analysis of a dolerite from this area 
appears in column 4. 
TABLE 1. 
Analyses of Basic Rocks from fhe Toodyay Area. 
SiOg 
A1,03 
Fe^Os 
FeO 
MgO 
CaO 
Na^O 
K^O 
H 3 O+ 
H.,0- 
TiO, 
P2O; 
MnO 
b^eS.> 
Norms. 
Q 
Or 
Ab 
An 
di 
iiy 
mg 
il 
ap 
py 
1 . 
2 . 
3. 
4. 
53-61 
50-20 
49-05 
49-13 
10-77 
15-00 
15-03 
13-13 
2-21 
3-83 
3-16 
3-65 
9-02 
8-93 
9-08 
8-95 
6-92 
6-04 
6-96 
7-64 
10-04 
10-65 
10-47 
11-84 
2-12 
1-90 
1-70 
1-72 
1-54 
0-07 
0-95 
0-16 
1-62 
1-62 
1-43 
1-72 
0-17 
0-07 
0-25 
0-04 
1-05 
1-06 
1-07 
1-27 
0-17 
0-12 
0-08 
0-14 
0-35 
0-16 
0-09 
0-15 
n.d. 
n.d. 
0-13 
0-45 
99-59 
99-65 
99-45 
99-99 
5-10 
6-18 
1-98 
3-48 
8-90 
0-56 
5-56 
1-11 
17-82 
16-24 
14-15 
14-15 
15-57 
31-97 
30-58 
27-52 
27-30 
16-41 
16-68 
24-88 
17-52 
19-18 
21-58 
18-33 
3-25 
5-57 
4-64 
5-34 
1-98 
2-13 
2-13 
2-43 
0-34 
0-34 
0-34 
0-34 
— 
— 
0-13 
0-45 
1. Schistose plagioclase amphibolite (15437), interbedded with quartzite, Toodyay, W.A. 
2. Schistose plagioclase amphibolite (1241), xenolith in Upper granite gneiss, Toodyay, 
W^. A. 
3. Coarse granular quartz-plagioclase amphibolite (15441), xenolith in Lower granite 
gneiss, Toodyay, ^^^A. 
4. Quartz dolerite (15424), dyke in metamorphic rocks, Toodyay, W.A. 
All analyses by R. T. Prider. 
Amongst the rocks forming this band there is, as j)reviously noted, but 
little variation. Microcline may be absent and ([uartz may be more abundant 
than in the tyj>e rock. Iron ore rimmed with spliene, indicating its origin 
from ilmenite, is a common feature, although in the rock described above 
the usual (‘entral ore inclusion in the S])hene is absent. 
T'he most unusual variant of the plagioclase amphibolites is a type in whicli 
diopside finds considerable development. 15440 is typical— it appears in 
hand sjjecimen to be a normal hornblende schist with narrow bands and 
lenticles (never more than 2 mm. wide) of light greenish diopside. 
