precious opal of good quality, and by careful search the opal was discovered in situ. In
1890 several mineral leases were applied for, and since that time a
large quantity of opals have been obtained there. In 1892 one
leaseholder raised about 500 oz. of precious opal, valued at over
£2,000. Some of the opal from this field has realised as much as £18
per oz. In the early part of 1893 about twenty miners were working the
various properties with a fair amount of success. During that year
mining for opal was so successful that a township sprang up, the
population being estimated at about 700 persons. The sum realised from
the sale of the opal raised during 1893 at this locality was £17,000,
some very fine stones being obtained. The opal is found at an average
depth of from 10 to 12 feet from the surface, although in some
instances it has been obtained at a greater depth. Mr. Pittman, the
Government Geologist, believes that the opal will be found at greater
depths. The surface is a red clay, beneath this is a layer of gypsum,
and then about 2 feet of hard sandstone, below this the opal-bearing
rock is found. The ground is also worked when possible by open-cuttings.
Fossil remains are found here altered into precious opal.
There
appears to be little doubt that opals exist plentifully over this
portion of the Colony, and eventually when the demand for these gems
shall have increased, a good trade will be done, and perhaps a
profitable industry be established. Large areas of opal country are as
yet untouched, although much opal was recovered during the year 1891.
Among
the large historical specimens of the opal may be mentioned the one at
Vienna, found in 1770, at Czernowitz ; it weighs 17 oz., and although
having many defects, it is stated that the sum of £10,000 has been
refused for it.
Perhaps
the most remarkable opal ever recorded was the one owned by the Empress
Josephiue ; this was known as the " Burning of Troy," because of the
red flames on its surface, giving it the appearance of being on fire.
The under side of this gem was opaque, a peculiarity often observed in
the Honduras opal; the upper portion was transparent, through which the
fiery rays were seen.
There
were some very valuable opals in the Hope collection; one engraved with
the head of Apollo is supposed to be of great antiquity.
The
opal is cut upon a leaden wheel with emery, and polished on a wooden
wheel with tripoli powder and water, and lastly with felt. Great care
has to be taken not to heat the stone too much by friction. They are
cut en cabochon, both sides often being convex.
It
is a difficult matter to engrave opals, on account of their brittle
nature, but some fine engraved specimens are in existence.
Unfortunately
the opal is, for a precious stone, low in the scale of hardness, and
is not desirable for rings on that account; but it is largely used for
bracelets, pendants, and ornaments for the head. It is very liable to
be injured by contact with oily or greasy substances.
The
value of the precious opal depends entirely upon its brilliancy and
play of colours. The prices given by Mr. Streeter are as follows :—
The smallest stones, £1 to £1 10s. per carat, medium stones, £2 to £3 „
larger stones, £3 to £5 „
Specimens of good size and purity, on account of their extreme rarity, are very valuable.
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