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Jet (lignite)
Jet is a type of lignite, a precursor to coal, and is considered to be a minor gemstone. Jet is not considered a true mineral, but rather a mineraloid as it has an organic origin, being derived from decaying wood under extreme pressure.
The English noun "jet" derives from the French word for the same material: ''jaiet''.〔''Oxford English Dictionary'' (2nd edition) 1989, Oxford, Oxford University Press〕 Jet is either black or dark brown, but may contain pyrite inclusions,〔Pye, K. (1985) ''Electron microscope analysis of zoned dolomite rhombs in the Jet Rock Formation (Lower Toarcian) of the Whitby area, U.K.'', Geological Magazine, volume 122, pp. 279–286, Cambridge University Press, 〕 which are of brassy colour and metallic lustre. The adjective "jet-black", meaning as dark a black as possible, derives from this material.
==Origin==
Jet is a product of high pressure decomposition of wood from millions of years ago, commonly the wood of trees of the family Araucariaceae. Jet is found in two forms, hard and soft. Hard jet is the result of the carbon compression and salt water; soft jet is the result of the carbon compression and fresh water.
The jet found at Whitby, in England, is of early Jurassic (Toarcian) age, approximately 182 million years old.〔Cope, J. C. W. (2006) ''Jurassic: the returning seas'' - plate 26 and page 339 of Brenchley, P. J. and Rawson P. F. (editors) (2006) ''The Geology of England and Wales'', 2nd edition, London, The Geological Society〕〔("Jurassic timescale" ). Retrieved 2010-06-23.〕 Whitby Jet is the fossilized wood from species similar to the extant Chile pine or Monkey Puzzle tree (''Araucaria araucana'').〔Oliver, N., 2012, ''A History of Ancient Britain'', Phoenix Paperback, ISBN 978-0753828861〕
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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