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Topazius, Peridot

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314                 NATURAL HISTORY OF GEMS.
neighbourhood of the Egyptian Thebes ; and the lapidaries accurately discriminated the two varieties the Chrysopteron, our Chrysolite ; and the Prasoides, our Peridot ; the latter " aiming at the exact imitation of the colour of the leek-leaf." For, although chemically the same, both being Silicates of Magnesia coloured by Protoxide of Iron, yet, from the jeweller's point of view, there is a great difference between the Chrysolite and the Peridot. The former is somewhat harder, and the yellow in it greatly predominates over the green : it possesses much of the Diamond's lustre, which it exactly resembles by candle-light, when that greenish-yellow tinge is no longer discernible. The Chrysoberyl of the mineralogist, an extremely hard combi­nation of alumina with small proportions of glucina and silica (whence its superiority in hardness to the other Beryls) is universally known in the trade by no other name than " oriental " Chrysolite. Science, again, restricts the designation of " Peridot " to the softer silicate of magnesia. In the Peridot green is the predominant colour, but slightly modified by yellow ; in fact, in the rough it much re­sembles a rolled pebble of bottle-glass, or a " Brighton Emerald." * No wonder that the gem so greatly charmed the Greeks, whose sole method of cutting coloured stones •was en cabochon·, few others approach it in lustre and richness of hue, and but for its extreme softness it would still hold a high place in the rank of precious stones, f
This substance is polished with great difficulty, and only by the use of tripoli moistened with vitriol upon a leaden wheel, a secret discovered in Europe not before the last
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