The finest opal known is obtained in the Upper Cretaceous formation at White Cliffs, near Wilcannia, New South Wales, and at these mines about 700 men find constant employment.
Other precious stones, including the sapphire, emerald, oriental emerald, ruby, opal, amethyst, garnet, chrysolite, topaz, cairngorm, onyx, zircon, etc., have been found in the gold and tin bearing drifts and river gravels in numerous localities throughout the states.
The opal was mined here Boo years ago, and the largest piece hitherto found, weighing 2940 carats and estimated to have a value of £175,000, is preserved in the Court Museum at Vienna.
For other forms of silica see OPAL and TRIDYMITE.
Hungary is the only country in Europe where the opal is found, namely at the famous mines of Vorosvagas in the county of Sáros, and at NagyMihaly in that of Zemplin.