[3] Jet is either black or dark brown, but may contain pyrite inclusions[4] which are of brassy colour and metallic lustre.

[5] Despite the name they both occupy the same area of the Mohs scale with the difference being that soft jet is more likely to crack when exposed to changes in temperature.

[7] Jet is very easily cut using carving tools, but small pieces tend to break off, making it difficult to create fine details.

This jet deposit was formed approximately 181 million years ago, during the Toarcian age of the Early Jurassic epoch.

[10][11][12] Whitby Jet is the fossilized wood from species similar to the extant Chilean pine (Araucaria araucana).

[16] The jet found in Asturias, the biggest deposit in northern Spain,[17] is of Late Jurassic (Kimmeridgian) age, about 155 million years old.

Asturian jet is a perhydrous coal that suffered an anomalous coalification process and presents great material stability over long periods of time.

Santiago de Compostela was the main sales point and the location of the workshops that produced artistic objects.

Jet has also been extracted in the area of Utrillas, Gargallo, and Montalbán in the province of Teruel, although it is of lower quality than that from Asturias.

[19] Native American Navajo and Pueblo tribes of New Mexico were using regionally mined jet for jewelry and the ornamentation of weapons when early Spanish explorers reached the area in the 1500s.

[24] The earliest known worked jet object is a 10,000 BC model of a botfly larva, from Baden-Württemberg, Germany, found among the Venuses of Petersfels.

[35] The Roman period saw its use as a magical material, frequently used in amulets and pendants because of its supposed protective qualities and ability to deflect the gaze of the evil eye.

Vikings made some use of jet including rings and miniature sculptures of animals with snakes being a prominent theme.

[46] It originally became fashionable in the 1850s after the queen wore a necklace of it as part of mourning dress for Princess Victoria of Saxe-Coburg and Gotha.

[50] While jet substitutes may have had an impact this appears to have been in a large part due to changes in fashion with Art Nouveau making little use of black jewellery.

[50] As the numbers fell the remaining manufactures tended to stick with existing styles rather than attempting to adapt to new fashions resulting in demand falling further.

[50] Making tourist trinkets kept a few jewellers in work, but by the end of World War II only three remained, and the industry died out completely with their deaths.

When rubbed against unglazed porcelain, true jet will leave a brown streak, although bog oak, vulcanite, and lignite will do the same.