Jet is a type of lignite, not a mineral, but is rather a mineraloid.
A mineraloid is a naturally occurring, inorganic solid that does not exhibit crystallinity. It may have the outward appearance of a mineral, but it does not have the "ordered atomic structure" required to meet the definition of a mineral. Colour is dark with brassy coloured surface and metallic lustre.
Jet is a product of decomposition of wood from millions of years ago, commonly from the the wood of trees of the family Araucariaceae, the Pine-like conifer tree.
Jet is around 75% carbon and 12% oxygen with sulfur and hydrogen making up most of the balance . Jet has a Mohs hardness ranging between 2.5 and 4 and a specific gravity of 1.30 to 1.34, making it very light-weight The refractive index of jet is approximately 1.66. The touch of a red-hot needle should cause jet to emit an odour similar to coal. The same test is used to authenticate Ancient Amber and Copal whose scent is that of Pine.
Jet may induce an electric charge like that of Amber when rubbed.
