Jet

Jet is a geological material that is not considered a mineral in the true sense of the word, but rather, a mineraloid. It is a hard, compact variety of lignite, coal-black in color. It is easily polished and has been used in the manufacture of jewellery, especially for mourning. The adjective jet-black is perhaps more well-known than is this mineral from which it is derived.

Jet as a gem material reached the height of its popularity during the reign of Queen Victoria (as she wore it as part of her mourning dress). Although now much less popular, authentic jet jewels are valued by collectors. Anthracite and vulcanite are similar materials that have been used to imitate fine jet: these imitations are not always easy to distinguish from the real thing, requiring destructive testing to be certain.