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.Discussed in part II of: L.B. Railsback Definitions   and  

The English noun "jet" comes from the French word for the same material: jaiet.Oxford English Dictionary 1989. 2nd ed, 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, 122, 279-286.  which are of brassy colour and metallic lustre. The adjective jet-black, meaning as dark a black as possible, comes from this material.

 References 

Category:Organic minerals
Category:Gemstones