OPAL. This delicate iridescent gem has been known by the name it now bears from the time of Pliny. There is in it the gentler fire of the ruby, the brilliant purple of the amethyst, and the sea-green of the emerald, all shining together. This is produced by the reflection and the refrac tion of light in certain openings of the mass. Opal seems to have been first brought from the Indus, but Arabia and Ceylon have been named ; Saxony, Hungary, Ireland, Iceland, Scotland, and Mexico are now known to yield it. The best oriental opal is from Hungary. Fire opal, in particular, comes from Mexico. In Hungary, its most celebrated locality is the village of Tcher venitza in the trachytic range, extending between Tokaj and Eperies. These mines have been wrought for many ages. The fire opal, of a beautiful topaz-yellow colour, with great lustre, is not obtainable in large masses.
Precious opal is the most beautiful of all gems. Its price depends on the play of colours dis played. The hydrophane loses its beauty when A expo3ed to water. Opal generally contains a little oxide of iron, and a small quantity of the alkaline earths. Precious opal scratches glass,
but is easily broken, on account of the numerous fissures by which it is traversed, and which pro bably give rise to the play of colours. Opals are cut with rounded faces. Common opal, or semi opal, has not the hardness of opal, and is easily scratched by glass, which distinguishes it from silicious stones ; it is called semi - opal. Opal jasper resembles jasper, but contains iron, and is not so hard. Ilungarian opals are the more valu able and harder ; they present a uniform milkiness of surface, more or less iridescent. The Mexican opals, when recent, present an unmixed globule of green fire, but they become colourless or of au opaque brown if wetted. The opal is only cut in cabuchon. The opal of Nonius, which Mark Antony proscribed, was valued at £20,000 of British money. According to Pliny, India was the source of opal. Common opal occurs in the volcanic rocks of the Dekhan.—Jani. Ed. Jour.; King ; Tavernier's Tr.; Eng. Cyc. ; Tomlinson.