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GEMS AND PRECIOUS STONES.
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away under that impression. The following will serve to illustrate the advantage of being able to determine these gems : A large mass of white topaz, now in the British Museum collection, was at one time used as a door-stop by a marine store dealer in London. He sold it for 3s. It weighs 12 lb. avoirdupois.
It has been stated that the topazes taken from the beds of the rivers at Capao, in Brazil, secured a net profit of £3,000 in twelve years.
At present the commercial value of the topaz is small. A stone of good size and of good colour may be purchased for a pound or two, while smaller stones, in the rough, are only worth a few shillings per pound avoirdupois ; still they are of some value, and worthy of collection, especially in the New England District of New South Wales, where they are plentifully distribu­ted. Good pink stones (which, of course, are manufactured from topazes having a suitable colour) are worth from about £2 per ounce. In some parts of India the topaz is of far greater value than in England.
Tavernier describes a topaz, weighing 157 carats, belonging to the Emperor Aurungzeb, an Indian monarch, which had been purchased by him for the large sum of £18,000. This might hare been an " Oriental topaz."
Formerly these gems were of far more value, but fashions change and tastes differ; and gem stones, being used principally for ornamental pur­poses, are entirely at the mercy of fickle fancy.
The topaz has been occasionally used by the engraver, even from very early times, intaglios being in existence of early Greek workmanship. An antique engraving, bearing a cluster of stars, in the St. Petersburg collec­tion ; the portraits of Phillip II. and Don Carlos, engraved on a topaz, in the Royal Library of Paris ; and the engraved seal ring owned by the Emperor Hadrian, are among the few engraved specimens of this gem. It does not appear to have been generally in favour for work of this class.
Topaz is cut on a leaden wheel with emery, and polished with tripoli pow­der. The best form of cutting is as a " brilliant " having the table smaller than in the diamond. The large so-called diamond in the Portuguese Trea­sury is supposed to be a topaz ; it is as large as a hen's egg.
The topaz is found in almost every part of the world, and in Saxony constitutes massive rocks, known as " topaz fels." Often this gem is associated with granite and gneiss, and usually some fluorine is contained in these rocks. In the Urals it is found in granite. In Brazil it is found in a loose sandy clay. Some beautiful blue specimens have been found in Colorado, in the United States ; pale violet in Saxony ; sea-green, sometimes known as aquamarine, in Bohemia; blue in Scotland; while Brazilian specimens are found of nearly all colours.
The topaz is, when crystallized, found as rhombic prisms, usually having but one end regularly terminated. When thus seen it cannot be mistaken for quartz, which crystallizes in the hexagonal system ; nor for the yellow sapphire, which is also hexagonal. This difference in crystalline form, together with the perfect basal cleavage of topaz, and difference in hard­ness, are usually quite sufficient to determine the topaz; even in waterworn pebbles a flat portion is usually seen where the topaz has cleaved.
Very fine topazes occur in the southern portion of the Urals, in the Ilmen Hills. They are also found in the Mourzinsk deposits in the north-east of Ekaterinburg. The largest topaz known was found here. It is now in the museum of the Mining Institute. It measures 27 centimetres (about 10-1/2 inches) in length, and 31 centimetres (about 12 inches) in circumference.
The topaz is common in New South Wales, especially in localities where tin is obtained, and specimens have been found of large size, especially those from near Mudgee.