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Ch. 7: Corundum: Sapphire Rubies etc.

Ch. 7: Corundum: Sapphire Rubies etc. Page of 149 Ch. 7: Corundum: Sapphire Rubies etc. Text size:minus plus Restore normal size   Mail page  Print this page
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PRECIOUS STONES.
The specific gravity of pure, transparent corundum including the colourless, yellow; red and blue varieties, is as nearly as possible 4, the extremes being about 3·07 and 4.05 respectively. A fine yellow stone without flaws gave 4.006.
All corundums possessing a distinct colour aie invariably dichroic. By this property rubies can be at once discriminated not only from garnets, but also from spinels. The dichroiscope shows, with the true ruby only, two differently coloured squares. Similarly the sapphire can be thus distinguished trom the blue spind, and of course from blue paste. The twin-colours, polarised in opposite planes, are these—
There can be no doubt that part, at least, of the peculiar beauty of fine rubies and sapphires is due to the play of different hues caused by their dichroism.
The ruby, when of perfect colour and fair size, is more valuable than any other precious stone save the emerald. If a diamond of five carats be worth £350, a faultless ruby of the same weight would sell for £3000 at least. A very fine stone of a single carat may be worth as much as £100. All or nearly all the fine rubies met with in collections are believed to have come from Burma. The district of Mogok, in Upper Burma, in a mountainous region, includes the most important ruby-tract. The town of Mogok is itself ninety miles N.N.E. of Mandalay. Two very fine stones from this lccalitv reached England in 1875. When reçut they weighed 32-3/16 and 39-9/16 carats respectively. The rubies from Siam are, as a rule, not only too dark in colour, even verging on a brownish red, but they are also slightly cloudy. A large cut ruby, probably from Burma,was offered for sale at Christie's auction rooms on May 7, 1896. It weighed 46-3/4 carats ,and was of an oblong form : its colour was
Ch. 7: Corundum: Sapphire Rubies etc. Page of 149 Ch. 7: Corundum: Sapphire Rubies etc.
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