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184
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GEMS.
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largely
red, green, and black porphyries, which they procured from Egypt and
Arabia, and many of their sarcophagi, statues, busts, and columns
composed of this stone, now adorn our museums.
Antique
porphyries were often of considerable dimensions, and in proof of this
we see the obelisk of Sixtus V. and the splendid columns of the church
of St. Sophia of Constantinople.
In the seventeenth century porphyry was still used all over Italy.
At
present porphyries are found in various regions of Europe, but, on
account of their hardness, they are only used in works of art, or for
utensils, as mortars, palettes, and stones for grinding colours.
In
1823 two Englishmen, named Burton and Wilkinson, discovered the great
caverns which supplied porphyry to the ancients, and which are situated
in a group of mountains, about twenty-five miles from the Eed Sea, and
called Djebel Dokhan.
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LXXXIII.
PRASE.
Prase is a diaphanous mineral, semi-transparent, and not very hard, and on account of its colour is called prase, or prasina, from the Greek πράσον, leek, because it is green as the leaves of the onion.
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