Jet is organic in origin. Like coal, it was formed from the remains of wood immersed in stagnant water millions of years ago, then compacted and fossilized by the pressures of burial. Jet is black or dark brown, but may contain pyrite inclusions which have a brassy color and metallic luster. Jet takes a good polish, and is often faceted. When burned or touched with a hot needle, it exudes the characteristic smell of coal.

Evidence suggests that jet has been mined since about 1400 BC, and worked pieces of jet have been found in prehistory burial mounds. During the Roman occupation of the British Isles, worked pieces of jet were shipped to Rome. Perhaps the most famous historical source is Whit by in Yorkshire, England, where much of the jet that was so popular for the mourning jewellery of the 19th century originated. During this time the mining and fashioning of jet provided the town with much of its income. Other localities include Spain. France, Germany. Poland. India. Turkey, the former USSR, China, and the USA.

Jet was popular for mourning jewellery in the 19th century due to its somber color and modest appearance, and traditionally it has been fashioned into rosaries for monks. Jet has also been known as black amber, as it may induce an electric charge, like that of amber, when rubbed. Powdered jet added to water or wine was believed to have medicinal Power.