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.
These stones are considered by some writers as varieties of quartz ([76]), and by others as a kind of opal ([102]). They are sometimes found in Hanover, but are chiefly brought from the island of Ceylon. It is usual to cut them before they are exported, and generally in a convex and oblong form, without facets, and in such manner as to bring the streak which intersects them into the centre. Among the king of Candy’s jewels, which were sold by auction in London, in June 1820, was a cat’s-eye of extraordinary magnitude and beauty. It was two inches in diameter, of dark colour, and nearly hemispherical. This stone was set in gold, with small rubies round it, and was sold for more than 400l.
Cat’s-eyes are chiefly used for setting in rings. Their size seldom exceeds that of a hazel nut; but there was one in the cabinet of the Dukes of Tuscany, which was nearly an inch in diameter. Those that are the most highly esteemed are of an olive-green, or red colour.
87. WOODSTONE is a very hard mineral substance, supposed to have been wood petrified with a siliceous mineral called hornstone.
It is of various colours; and has not only the external appearance, but the internal organization of wood.