The Geology and Physiography of the Lawnswood Area. 
63 
(i) The amphibolites are dark, grey-green medium- to coarse-grained, 
melanocratic rocks containing hornblende, plagioclase and diopside with 
accessory biotite, apatite, cpiartz, and sphene and are almost identical 
mineralogically with the hornblende schists ot the metasediments. There 
are. both granulose and schistose varieties. 
Granulose quartz-plagioclase amphil)olite3 (22524) are dark grey, 
uniform textured rocks with a medium to coarse grain and a granoblastic 
mierostructure. The minerals present are intensely pleochroic blue-green 
hornblende (c A ^ — 21°, 1.672), basic oligoclase (saussuritised 
and with normal gradational zoning occasionally developed), strongly 
pleochroic greenish-broAvn biotite, rpiartz, and accessory apatite, radio- 
active titanite, actinolite and diopside. 
The approximate conqmsition is hornblende 05 per cent., oligoclase 
25 per cent., biotite live 2 )er cent., (iuartz three i)er cent., titanite two 
per cent. 
The schistose (luartz-diopside-plagioclase amphibolites (19188) differ 
from the above in their schistose structure and greenish-grey colour due 
to the presence of green diopside which sometimes forms more than 10 
per cent, of the rock. Tin* liornlilende is similar to th.at in the granulose 
amphibolites (e A ^ ” 24°, ^ = 1.675) ; andesine (Ah^ AnJ is the 
plagioclase present; and the diopside is a green variety with very feeble 
pleochroism, (-j-) 2V large, e A — 41°. 
(ii) The quartz-plagioclase-epidote-clilorite rock (22487) is greenish- 
grey with a uniform texture and fine grain. Occasional veinlets of paie 
yellow-green epidote are seen in the rock. The minerals are a very dark 
green platy chlorite, average grain size 0.5 mm., veinlets and aggregates 
of pale yellow green epidote, equidimensional white grains of felspar 0.5 
-1.0 mm. in diameter. There is a slight Ijanding caused by the parallelism 
of the ciilorite plates. 
A chemical analysis of 22487 (Table 2, T) shows that except for higher 
8iO. and AlA), and the propoifional lowering of the other constituents the 
rock chemically resembles a hornblende .schist xenolith (Table 2, II) in the 
gneiss from Toodyay (23, p. 105). 
The rock Ls a rare type as shown by the quantitative classification 
(II, 4, 5), only one comparable rock, a gabbro, being listed in a.shington’s 
^Themical Analyses of Igneous Rocks” (28, p. 419). 
The compo.sition except for the high SiO. is somewhat similar to that 
of quartz dolerite so that the rock might be the result of the granitization 
of a basic igneous rock. 
The rock (22487) has a granoblastic microstructuix with a tendency to 
be finely gneissic. The (]uartz is generally clear with an irregular form. 
Inclusions of chlorite are rare and an intergTOwth of quartz and untwinned 
plagioclase is sometimes obser^’ed. Chlorite is green, practically isotropic 
with occasional grey blue anomalous inlerPerence colours and weak pleo- 
chroism from green to light yelloAV gi'cen. It ap]>ears to be pseudomorpliie 
after an ampbihole as it occurs in forms similar to the typical amphibole 
basal section and occasional bands of epidote cross the chlorite at angles 
