83. YELLOW, _or_ TOPAZINE CRYSTAL _is a stone of wine─yellow colour_. It is found in Brazil and Bohemia, but has no other alliance with the true topaz than its colour. 84. CAIRN GORUM CRYSTALS are obtained in various parts of Scotland, but particularly from a mountain of that name in the county of Aberdeen. _They are usually of smoky yellow or brown colour_, and are, at this time, so much in request for ornamental articles of dress, that several lapidaries have been induced to settle in Aberdeen, who are constantly employed in cutting them for seals, rings, necklaces, brooches, and other trinkets. When these crystals are of deep and good colour, they are nearly as estimable as topazes; and, if clear and large, they are sold at a high rate. The price of inferior seal─stones varies from ten shillings to three or four pounds each; but those of superior beauty will produce from five to ten guineas. Such specimens as have a pure and full yellow colour are often sold for topazes. When they are muddy, the lapidaries have the art of entirely dissipating the colour, and giving them a transparent lustre. This is done by means of heat, which will dissipate the colour of every species of crystal. 85. _AVANTURINE is a quartz, generally of reddish colour, sprinkled with yellowish shining points of mica (123), which are dispersed through its whole substance._ A French artist, some years ago, having by accident, or “par aventure,” suffered a quantity of brass filings to fall into a vessel of melted glass, afterwards found that it was admirably calculated for vases and different kinds of ornamental work. Hence he denominated it avanturine, a name which mineralogists have since applied to those natural objects of which this production of art was an apparent imitation. Avanturine is found in some of the countries bordering upon the White Sea, in Spain, and some parts of France. In the late Leverian Museum there was a piece which weighed near five pounds, and was unique both for beauty and magnitude. It had been discovered in 1788, amongst the ruins of the triumphal arch of Julius Cæsar in the valley of Suse, in Piedmont; and was purchased of the person who found it for 200 guineas. Avanturine is cut into various ornamental articles, which are sometimes sold at a very high price. Imitations of it are very common, and are formed by the simple operation of throwing brass or copper filings into coloured glass in a state of fusion. 86. _CATS─EYE is a stone of brownish grey colour, tinged with green, yellow, white, or red; semi─transparent, and reflecting from its interior a splendid white line or speck, which_ _varies according to the direction in which the stone is held to the light._ _It is found in pieces that are rounded, massive, or blunt─edged._