Mineralogy of the Donnybrook Sandstones 
Western Australia. 
215 
Zircon-. Zircon is a i)roniiiient constituent in all the residues. Colourless, 
worn grains predominate, and many of these lia\‘e larg'o inclusions of bubbles 
and rods; zoning is not a common featuj'e, but occasionally linely-zoned grains 
occur. Purple zircon is race, odd grains only being recorded from spGf'imeus 
(), 13, 18, 25, and 4005. The most deeply coloured grains are pleoehroi(' 
from a brownish-purph* to dee[) puri)le and arc* similar to those found in 
other sediments in south-westeni Australia, l^irple zircon is known as an 
accessory in some of the Pre-Cambrian gneisses. Tawny or brownish zircons, 
possibly derived from the same source as the pTirple, were obtaijied in 
specimens J, 3, 12, 13, 15, and 10. Most of the zir('on grains are more or 
less rounded but sonu' shar])-edged mystals also occur. The r<)unding indicates 
considerable transport, and possibly more than one cych' of sedimentation. 
Tourmaline occurs in a variety of colours sucli as bright yellowish-brown, 
grey, })inkish-grey, or i)ijikish-])rown, and blu(‘, tluj latter being seance. Al- 
though tourmaline is a noticeable constituent because of its colour, it does 
not make uj) a great i)art of each residue and little signiticance can be 
attached to it except to note that some ol‘ the grains are well-rounded and 
spherical, and hence are probably sin-vivals, along witli the rounded zircon, 
from other cycles of sedimentation. 
Although the Pre-Cambrian rocks in the Prt^stou Valley to tlu^ east of, 
and not far from, I)onnyl)rook are comparatively rich in touiaualiiie, yet 
it is not a major constitmmt of the Donnybrook sandstone residues. This 
is one reason for believing that the Donnybrook sandstones have not been 
derived from local sources. 
Rutile is a fairly prominent constituent. The grains are generally robust 
and rounded, and of deep reddish-brown colour. In some specimens yelloAvish- 
brown grains are also ]:)resent, but th(*se show very few signs of wear and 
transport. Yt'llowish-browji, broken, geniculatt' twins are found occasionally. 
Anata^e: As shown in Table 1, anatase is pi’eseut in about one-third of 
the specimens. The grains generally vary from st(‘el-gi‘ey to pale yellow in 
('olour, but occasionally steel-blue ones are to be found. Both the tabular and 
octahedral habits occur, the tabular being th(‘ mor(‘ common. Anatase is 
present only in very small amounts and it must l)e regarded as an authigunic 
constituent for the grains are euluHlral, unworn, and sometimes two or more 
small crystals are joined together. 
Sphene is fairly plentiful in ang'ulai', colourless fragments of ^'chunky” 
appearance. Jt is a constituent of practically all the specimens examined. 
Monazite in j)aie yellowish-green Avorn grains is chai’acteristic of a 
number of residues. Its presence is to be expected Avhere granitic material 
has been incorporated in a sediment. 
Epidotc and zoisite: Epidote in pale yelloAvish-green, somcAvhat worn 
grains occurs in about three-(piarters of the specimens, but zoisite Avas only 
recorded in two residues, Epidotc nevt'v makes up a large inirt of any 
residue, and is usually restricted to a feAv grains. 
Amphihole is present in about the same amount as epidote or less and 
often there are only one or tAvo grains to each slide. The amphibole is the 
bright bluish-green variety common to the hornblende schists and epidiorites 
of the Pi'e-Cambrian complex. That it is not present in greater quantities 
indicates that greenstones Avere not being actively eroded during the forma- 
tion and deposition of the Donnybrook sandstones, for it is a resistant mineral 
and not easily broken doAvn by Aveathering. Ils scarcity also suggests deri- 
