the
colours do not change so much when the stone is moved. The sub-variety,
Lechosos-Opal, which occurs here, shows specks of emerald-green and
carmine.
In
New South "Wales, in a decomposed amygdaloidal volcanic rock, Precious
Opal occurs, associated with other forms of Opal; this is at Rocky
Bridge Creek, in Georgina County. Also at White Cliffs, Yungnulgra
County, there is a deposit of considerable importance, both because of
its commercial value and also on account of its peculiar matrix, which
is a white sandstone. The Precious Opal, along with common Opal, occurs
in the joint- and bedding-planes of the rock. Cretaceous fossils are
found in some cases filled with Precious Opal, and fetch very high
prices as curiosities; it also is found pseudo-morphous after Gypsum
(E. F. Pittman).
In
Queensland, at Bulla Creek, Precious Opal again is found in a silicious
rock, in this instance a highly ferruginous sandstone, in the fissures
of which it occurs in thin layers in association with common Opal. The
colour of this Opal is of a deep blue in general, with large areas of
the same shade nearly ; it of course has the green and red " fire."
2.
Fire Opal is of a reddish tint from the presence of ferric oxide, but
it may show the same play of colour as Precious Opal. The name refers
to its red colour, and on the same account it is sometimes called Sun
Opal. It is particularly liable to deteriorate through exposure. It is
found usually associated with other varieties at Zimapan in Mexico, in
Honduras, and in the Faroe Islands.
3.
Girasol is a bluish white variety with a rather feeble red "fire"; on
moving the stone a faint wave of bluish light may be seen to move
across it. It is found in the
