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See also: peculiar kind of See also: lignite or See also: anthracite; often cut and polished for ornaments
.
The word " See also: jet " probably comes, through O
.
Fr. jaiet, from the classical gagates, a word which was derived, according to See also: Pliny, from Gagas, in See also: Lycia, where jet, or a similar substance, was originally found
.
Jet was used in Britain in prehistoric times; many round barrows of the See also: Bronze age have yielded jet beads, buttons, rings, armlets and other ornaments
.
The abundance of jet in Britain is alluded to by Caius See also: Julius
See also: Solinus (fl
.
3rd century) and jet ornaments are found with See also: Roman See also: relics in Britain
.
Probably the supply was obtained from the See also: coast of See also: Yorkshire, especially near See also: Whitby, where nodules of jet were formerly picked up on the See also: shore
.
Caedmon refers to this jet, and at a later date it was used for See also: 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-See also: rock
.
The jet-rock series belongs to that division of the Upper See also: Lias which is termed the zone of See also: Ammonites serpentinus
.
Microscopic examination of jet occasionally reveals the structure of coniferous See also: wood, which A
.
C
.
Seward has shown to be araucarian . Probably masses of wood were brought down by a See also: river, and drifted out to See also: sea, where becoming See also: water-logged they sank, and became gradually buried in a deposit of See also: fine mud, which eventually hardened into shale
.
Under pressure, perhaps assisted by heat, and with exclusion of air, the wood suffered a peculiar kind of decomposition, probably modified by the presence of See also: salt water, as suggested by Percy E
.
Spielmann
.
Scales of See also: fish and other fossils of the jet-rock are frequently impregnated with bituminous products, which may replace the See also: original tissues
.
Drops of liquid See also: bitumen occur in the cavities of some fossils, whilst inflammable See also: gas is not uncommon in the jet-workings, and petroleum may be detected by its smell
.
Iron See also: pyrites is often associated with the jet
.
Formerly sufficient jet was found in loose pieces on the shore, set See also: 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 See also: 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 See also: moor-lands, such as Eskdale
.
The best jet has a See also: 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 See also: lathe, and sufficiently compact in texture to receive a high See also: polish
.
The final polish was formerly given by means of See also: rouge, which produces a beautiful velvety See also: surface, but rotten-See also: stone and lampblack are often employed instead
.
The softer kinds, not capable of being freely worked, are known as See also: bastard jet
.
A soft jet is obtained from the estuarine series of the See also: Lower Oolites of Yorkshire
.
Much jet is imported from See also: Spain, but it is generally less hard and lustrous than true Whitby jet
.
In Spain the chief locality is See also: Villaviciosa, in the province of See also: Asturias
.
See also: France furnishes jet, especially in the department of the See also: Aude
.
Much jet, too, occurs in the Lias of See also: Wurttemberg, and See also: works have been established for its utilization
.
In the See also: United States jet is known at many localities but is not systematically worked
.
Pennsylvanian anthracite, however, has been occasionally employed as a substitute
.
In like manner Scotch cannel See also: coal has been sometimes used at Whitby
.
Imitations of jet, or substitutes for it, are furnished by vulcanite, See also: glass, black See also: obsidian and black See also: onyx, or stained chalcedony
.
Jet is sometimes improperly termed black See also: amber, because like amber, though in less degree, it becomes electric by See also: friction
.
See P
.
E . Spielmann, " On the Origin of Jet," Chemical See also: News
(Dec
.
14, 1906) ; C
.
See also: Fox-Strangways, " The See also: Jurassic Rocks of
Britain, Vol
.
I
.
Yorkshire," Mem
.
Geol
.
Sure
.
(1892); J
.
A
.
See also: Bower,
" Whitby Jet and its Manufacture," Journ
.
See also: Soc
.
Arts (1874, vol. xxii. p . 8o) . |
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