12 
The Queensland Naturalist, 
July, 1921 
(Nos. 12, 13) Opals occur in Western Queensland 
over a ver\ large area of artesian water-bearing country 
in beds of cretaceous sandstone and other sedimentary 
rocks, and probably have been produced by the infiltra- 
tion of heated artesian water carrying silica in solution. 
The centres of opal-mining are very numerous, and gems 
of great value have been obtained in localities about 
Cunnamulla, Thargomindah, Eromanga, Kyabre, Jubdah, 
Adavale, Opal ton, and a host of other places, and 
developments which have taken place on the various 
fields show that the deposits of opal — good, bad, 
and indifferent — are practically inexhaustible. In 
South-Eastern Queensland the basalts of the Mc- 
Pherson Range and adjacent country are the source of 
opal occurring under entirely different conditions 10 
those prevailing in Western Districts. Similar volcamc 
rocks exist about Springsure, in the Central District, 
the opal occurring in flows of vesicular rhyolite. 
Specimen No. 12 is a dark harlequin opal from 
Tintenbar, taken out of decomposed basalt in Morris’s 
claim, and Specimen No. 13, the light-coloured green-pink 
opal, is ft* jm a sandstone at Cunnamulla. 
(Nos. 4, 5). Matrix opal is a hard ironstone 
originally made up of broken fragments, which subse- 
quently have been cemented together with opal. No. 
4 specimen is from Opalton, and No. 5 from Mainside, 
both Western Queensland localities. No doubt Queens- 
land offers great inducements for future mining devel- 
opments in opal. 
(No. 16). Chrysoprase is the apple-green chalcedony 
found in the shingle of Marlborough Creek, a branch of 
the Fitzroy River, about Yaarnba , some miles above 
Rockhampton The specimen in the collection contains 
a trace of nickel, which is probably the pale green 
colouring ingredient. Much of the stone found in the 
shingle has a greenish cloudy colour mixed with a milky 
chalcedony, but portions have a beautiful soft green 
colour which take a perfect polish. The source of the 
mineral is the serpentine country in the neighbourhood. 
(No. 26). Ribbonstone is a variety of jasper, usually 
having two or three shades of colour, varying between 
white, grey yellow, brown, and red. It has much the 
appearance of the grain of some woods, and because of 
this effect has been called “fossil wood,” although it is 
really of inorganic origin. So far as the Queensland 
ribbon jasper is concerned, the mineral is probably a 
