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.