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Jewelry News09/05/2008 09/05/2008 Refer a FriendStore Information |
Turquoise
 Turquoise has been used as an ornament since the dawn of history. Rich necklets and plaques of gold set with turquoise have been found in Egyptian and Sumerian tombs of the fourth millennium BC as well as beads of even greater antiquity. It was widely used by ancient civilization and in the Middle Ages and it retains great popularity to the present day. Turquoise is a phosphate of copper and aluminum containing some water. It is always found as crypto-crystalline aggregates and it fills fissures and cavities where rocks have weathered in the proximity of copper deposits. It is porous as well as soft and liable to discoloration by chemical agents. It should therefore be kept away from soap, sprays, detergents and any chemicals, as well as from dirt. Turquoise is usually impregnated with wax or resin after polishing to minimize the danger of loss of color. Since the most valuable color is a deep sky-blue, a dye is frequently added when treating material of mediocre quality to deepen natural tints and to overcome a tendency towards the less desirable greenish hues that many stones possess. The color of untreated stones is apt to fade after long exposure to sunlight. Some stones are veined with black limonite; when this veining is substantial the material is called turquoise matrix. The obvious style of cutting turquoise is as cabochons, but large pieces are polished flat. Gilt designs are sometimes incised into stones in the East. In Tibet and elsewhere, small but well-colored fragments are sometimes set closely together, held by pitch in a hollow mount of silver. Turquoise often looks to best advantage in a surround of small rubies. Turquoise is produced in Tibet, Iran. Some mines are in Turkestan. These mines were abandoned and the knowledge of their whereabouts lost for many centuries until their rediscovery in 1845; but little material has come from there for some time. The oldest mine in the USA is in New Mexico. Turquoise of greenish tint is stil obtained from that state. Few gemstones have been imitated as widely as turquoise. Even in ancient Egypt beads were made from blue faience, a kind of glazed earthenware, which resemble turquoise closely. They were made together with inserts for jewelry and such small items as scarabs, for thousands of years and similar products based on glass and ceramics are produced to the present day. Other imitations are made from a variety of powders similar to turquoise in composition and either compressed or bonded together with plastics. An exact synthesis of turquoise has been reported from Germany. Most of these artefacts can be distinguished by their lack of the characteristic absorption spectrum. This also applies to two natural minerals that somewhat resemble turquoise, namely variscite from Utah, which is green, often flecked with white, and odontolite, fossil bones, stained blue or green by phosphate of iron which often show signs of structure typical of bone. 
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