PRECIOUS STONES.
Pierre precieuse, . FR.Gemma, . . . . IT.
I Edelstein, . . . GER. Piedra preciosa, . . .Sr.
Precious stones are often termed gems by jewellers, who thus designate all minerals remark able for their hardness, lustre, and beauty ; but transparency, brilliancy, lustre, and freedom from defects, to be of great value, should also have associ ated with them the exact quantity of colouring to furnish the favoured tint. Besides the distinction of gems for the most beautiful of the minerals in jewellers' and lapidaries' work, under the term inferior gems' they utilize for ornamental pur poses many quartzose minerals, while pearls and nacre from molluscs are amongst the most esteemed of the gems, and coral from the animal, with jet and amber from the vegetable kingdoms, are much appreciated by many races.
If the precious stones in use as gems be noticed chemically, the diamond is a crystallized form of carbon ; the balas ruby and spinel ruby are compounds of alumina and magnesia ; the chrysoberyl and its variety Alexandrite are com binations of alumina and glucina ; the sapphire and ruby, the sesqui-oxide of aluminium ; the hyacinth and jargoon (zircon), a compound of silica and zirconia ; the beryl, emerald, and euclase, compound silicates of aluminium and glucinum ; tourmaline and rubellite, boro-silicate of several bases ; lapis-lazuli, a combination of silicate and sulphate of aluminium; and turquoise, a hydrated phosphate of aluminium ; amethyst, Bard, plasma, prase,.chalcedony, and noble opal are varieties of silica or quartz ; chrysolite and peridot, a silicate of magnesia and iron ; and garnets have a varied composition, containing two or more of calcium, magnesium, iron, man ganese, alu minium, chromium .
From the most ancient times all races have attributed fanciful virtues to them. The dia mond was considered by the Romans a remedy against incubus and succabos ; the ruby against poison ; jacinth procured sleep ; sapphire pro cured favour with princes ; it was on tables of sapphire that the ten commandments were en graved, and it was also supposed to preserve the sight ; the chrysolite assuaged wrath. Each of
the twelve apostles was symbolized with a precious stone,—Peter by jasper, John by emerald, and so on. A sardius was placed in the beast-plate of the Hebrew high priest ; any precious stone of a red hue was supposed by the Jews to be a pre servative against plague, and by the Arabs to be useful in stopping haemorrhage.
The value of these minerals varies. From their small hulk and consequent portability, gems have, always risen in price during wars. In the French revolution from 1789 to 1796, diamonds are stated by Mr. Emanuel to have doubled their usual price. The prices of the larger are also regulated by the demand and by the fancies of purchasers. The prices of gems seem always to have been higher in Asia than in Europe. Since the middle of the 19th century, fresh sources of precious stones have been discovered in Australia and at the Cape of Good Hope, and much alteration hag occurred in the prices. The most valued gems have been selling in India at 25 per cent. higher than In London. Yet India continues largely to export some kinds, and in the live years 185647 to 1860-61, the quantities exported ranged in value from £138,224 to £153,748 annually, nearly all being sent from Bombay, chiefly to Aden, Suez, which took about four-fifths, the rest to the United Kingdom, China, and France. Since then the exports amounted to Rs. 1,87,362 in 1882-83, and the imports rose to Rs. 36,82,177 in 1880-81.
Arabia is said to have the topaz, the onyx, and the yetnani or akik. The agate is found near Mocha, emeralds in the Hejaz, beryls and car nelian near San'aa and Aden, malachite in the cavern of Beni Salem ; also jasper, amethyst, and turquoise in the environs of the village of Safwa, about three days' journey from Medina. The diamond, the' sardonyx, and the topaz were ob tained through Arabia in ancient times.