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Onyx, Nicolo

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234
NATURAL HISTORY OF GEMS.
lapidary. Much more reason is there to suppose it the result of the incalculably better and more copious supply flowing in from a variety of sources now closed to us, such as Arabia, continually referred to by Pliny as producing the choicest gems, and the interior of Asia. Their Roman appellations inform us that this was the case with many of the ancient fine-coloured marbles, only known at present as existing in the remains of Caesarian magnificence ; such as the Rosso, the Nero, and the Giallo Antico, all from Numidia; the Paonazzo or Synnadic, from Phrygia; the Thebaic, fi'om Egypt, &c. Numidia and Ethiopia, perpetually quoted by Pliny as exporting marbles and gems of all kinds, are now completely lost to the trade, as also are the equally productive mines anciently skirting the Red Sea. In fact, these were the regions supplying the Greek gem-dealers before India was opened out to them; as Theophrastus distinctly states (34) : " First-class (precious) stones are rare, and come from only a few places ; such as Carthage and the country around Massilia (for amber and coral, doubtless), and out of Egypt, from Syene near the city of Elephantina, and from the district called Psephö, . . . and the stones used for inlaying-work, out of Bactria."
To return to the artificial colouring of gems, it is ascer­tained by experiment that those belonging to any species of translucent quartz, which have been rendered white and opaque by the action of fire, will in a great degree recover their original colours upon immersion in hot water. This fact is strikingly exemplified in a tricoloured Agate be­longing to myself, of which the two darker bands are com­pletely calcined and chalk-like, yet these, after a short soaking, again become of two shades of brown, and as translucent as ever. Winckelmann had noticed the same transformation in a stone ('Pierres Gravées,' No. 1123), engraved with an Apollo, which from white and opaque
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