232 QTARTZ FAMILY. colours to the greatest advantage: as it is soft, it should not be facetted ; but if facets are cut on it, these ought to be very flat. The cutting is done on a leaden wheel, with tripoli and water; and then the opal is rubbed with tin ashes, on a piece of chamois leather, by which operation it receives its perfect lustre. When it is de ficient in Colour, jewellers are in the practice of setting it in a foil of the desired colour; but if it exhibits a beautiful play of colour, it appears to the greatest ad vantage when set in a black case. At present, the opal is held in great estimation in all countries, but par ticularly in Hungary, Moldavia and Wallachia, where it forms the chief ornaments in the dress of the oldest and most wealthy families. It is exported to Turkey, and from thence it is frequently imported into Holland, where it is falsely denominated oriental opal. Jewels of opal must be very carefully kept, as this mineral easily scratches, and is very apt to crack on sudden changes of temperature. It was much prized by the ancients. Pliny (the only one of the ancient writers who mentions the opal) describes it as uniting the beauties of the car buncle, amethyst, and emerald; and the Greeks express ed their admiration of this lovely gem, by naming it pa- deros. Nonius, a Roman Senator, possessed an opal of extraordinary beauty, valued atTlfl0,000; rather than part with which to Mark Antony, he chose to suffer ex ile. He fled to Egypt with his opal, where it was sup posed he secreted it. It is not, after this, mentioned by any ancient writer; and the only other notice published in regard to it, is a story by a French interpreter lloboly, who pretended that he had discovered it amidst the ruins of Alexandria^, It