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Rh hues give rise to a brilliant orange light when apjflied to a copper-wheel charged with diamond dust in the operation of grinding. Then again the gold-coloured zircons having a density of about 4·4 continuously glow with a fine orange incandescence in the flame of a Bunsen-burner; this effect is apparently produced by the presence of thoria.

Ceylon yields the finest and largest specimens of precious zircon. New South Wales contains several deposits in which beautiful zircons occur: the stones from Mudgee have been known for some years. The zircons from Expailly in Auvergne are quite typical hyacinths; they possess a beautiful aurora-red hue, but are as a rule, very small. The market-value of the gem-varieties of zircon is small. Fine red columbine red and cinnamon-hued stones may be bought at 5s. per carat: yellow stones and dull green specimens are still cheaper, but the deep and rich leaf green stones and even those which are of a pale though pure green colour, as also those which are brilliantly white, bring larger sums. The largest "camellia-leaf" green zircon, weighing over 19 carats, with which I am acquainted brought 26s. the carat. But it was London-cut and no doubt weighed 5 or 6 carats more when imported in its native cut state. Such a stone, of the same high quality and colour and weighing 18½ carats cost £18 10s. in Ceylon: but it had to be re-cut and lost 2 carats in the operation.

White or colourless zircons are used in lieu of diamonds by wealthy natives in Ceylon. They have been employed in European jewellery also; sometimes a fine white zircon set in a massive ring of gold has been pawned as a brilliant, and not redeemed. A file will not scratch a facet of a zircon, so that this test for "paste" is inapplicable. But though much harder than glass, and harder even than rock crystal, zircon is unfortunately somewhat brittle, and easily becomes chipped in wear. An examination of a large number of engraved gems labelled hyacinth or jacinth has proved them not to be of true hyacinth, that is red zircon, but of garnet, either hessonite or cinnamon stone, or of almandine.