Jet is a fossilized organic substance very similar to coal, that is created from the same materials in the same way. The simplest way to tell if you have found a piece of Jet is to use it to draw a line on a hard stone: a faint brown line means you have Jet, a black line means you've found coal.
Jet may be one of the oldest of sacred gemstones. It is commonly found in prehistoric graves and seems to be associated with powerful women, Queens, Matriarchs and Pristesses. Jet symbolizes the power of the Goddess and the mystery of Night, in which the silver Moon is Queen. It can be polished to a high sheen using brass polish (and a lot of elbow grease!) and flat pieces of Jet make excellent magic mirrors that can be used in scrying and divination to gain Underworld knowledge. Jet was popular in Victorian England, worn as a stone of mourning during the reign of Queen Victoria, when mourning became strangely fashionable. Jet jewelry can be worn in honor of the Mighty Dead or during rituals that connect with the power of Underworld deities. Jet was the sacred stone of the Greek and Roman Mother Goddess Cybele - rub a piece of Jet and you can ask her for a favor.
Jet is said to be helpful for anyone who finds it hard to make decisions or to say 'no' when they ought to. A very shamanic stone, Jet can be used to increase intuitive knowledge of the Earth and totem animals, and is said to help the spirit body separate from the physical body for shamanic journeys and astral travel. According to an early writer Jet has eight virtues - it protects from storms and lightning, prevents poisoning, defends against sorcery, banishes demons from any home in which it is kept, an elixir given to one possessed by the 'hateful fiend' will reveal this and release them, a potion of it will restore health, the same potion restores a 'smooth body' and whosoever takes the potion is immune to snakebite.