Jet (lignite)

Jet is a type of lignite, a precursor to coal, and is a gemstone. Jet is not a mineral, but rather a mineraloid. 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: . Jet is either black or dark brown, but may contain pyrite inclusions, which are of brassy colour and metallic lustre. The adjective , meaning as dark a black as possible, derives from this material.

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. Whitby Jet is the fossilized wood from species similar to the extant Chile pine or Monkey Puzzle tree (Araucaria araucana).

Jet has been used in Britain since the Neolithic period, but the earliest known object is a 10,000 BC model of a botfly larva, from Baden-Württemberg, Germany. It continued in use in Britain through the Bronze Age where it was used for necklace beads. During the Iron Age jet went out of fashion until the early third century AD in Roman Britain. The End of Roman Britain marked the end of jet's ancient popularity until, despite sporadic use in the Anglo-Saxon and Viking periods, the later Medieval period. Jet saw a massive resurgence during the Victorian era.

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