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Encyclopedia Britannica - Main :: JEE-JUN |
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JET (Fr. jais, Ger. Gagat) , a substance which seems to be a peculiar kind of lignite or anthracite; often cut and polished for ornaments. The word " jet " probably comes, through O. Fr. jaiet, from the classical gagates, a word which was derived, according to Pliny, from Gagas, in Lycia, where jet, or a similar substance, was originally found. Jet was used in Britain in prehistoric times; many round barrows of the Bronze age have yielded jet beads, buttons, rings, armlets and other ornaments. The abundance of jet in Britain is alluded to by Caius Julius Solinus (fl. 3rd century) and jet ornaments are found with Roman relics in Britain. Probably the supply was obtained from the coast of Yorkshire, especially near Whitby, where nodules of jet were formerly picked up on the shore. Caedmon refers to this jet, and at a later date it was used for rosary beads by the monks of Whitby Abbey.The Whitby jet occurs in irregular masses, often of lenticular shape, embedded in hard shales known as jet-rock. The jet-rock series belongs to that division of the Upper Lias which is termed the zone of Ammonites serpentinus. Microscopic examination of jet occasionally reveals the structure of coniferous wood
wood
original
bitumen
Formerly sufficient jet was found in loose pieces on the shore, set free by the disintegration of the cliffs, or washed up from a submarine source. When this supply became insufficient, the rock was attacked by the jet-workers; ultimately the workings took the form of true mines, levels being driven into the shales not only at their outcrop in the cliffs but in some of the inland dales of the Yorkshire moor-lands, such as Eskdale. The best jet has a uniform black colour, and is hard, compact and homogeneous in texture, breaking with a conchoidal fracture. It must be tough enough to be readily carved or turned on the lathe, and sufficiently compact in texture to receive a high polish. The final polish was formerly given by means of rouge
series of the Lower Oolites of Yorkshire.Much jet is imported from Spain, but it is generally less hard and lustrous than true Whitby jet. In Spain the chief
Asturias
chalcedony . Jet is sometimes improperly termed black amber, because like amber, though in less degree, it becomes electric by friction.See P. E. Spielmann, " On the Origin of Jet," Chemical News (Dec. 14, 1906) ; C. Fox-Strangways, " The Jurassic Rocks of Britain, Vol. I. Yorkshire," Mem. Geol. Sure. (1892); J. A. Bower, " Whitby Jet and its Manufacture," Journ. Soc. Arts (1874, vol. xxii. p. 8o). End of Article: JET (Fr. jais, Ger. Gagat) If you wish, you can link directly to this article.
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