Jet (lignite)

Jet is a geological material considered to be a minor gemstone. It is originally a wood product called lignite, squeezed and heated by geological processes. The older definition of mineral did not apply to organic material. Therefore, jet was not called a mineral, but instead a mineraloid. However, this view is changing, as so many crystalline materials have organic origin.[1]

Mourning jewellery: Jet brooch, 19th century.
A sample of jet

The English noun "jet" comes from the French word for the same material: jaiet.[2] Jet is either black or dark brown, but may contain pyrite inclusions,[3] which are of brassy colour and metallic lustre. The adjective jet-black, meaning as dark a black as possible, comes from this material.

References
  1. Discussed in part II of: L.B. Railsback Definitions Archived 2013-03-02 at the Wayback Machine and Archived 2012-09-15 at the Wayback Machine
  2. Oxford English Dictionary 1989. 2nd ed, Oxford University Press.
  3. 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, 122, 279-286. doi:10.1017/S0016756800031496


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