Jet

Jet is not a true mineral but a mineraloid: a black, lightweight organic material formed from wood that was buried, compressed and fossilised into a hard, compact form of lignite coal. It takes a high polish and has been used for ornaments since prehistoric times.

Identifying jet

Jet is deep velvety black, lightweight, and warm to the touch compared with cold mineral 'black' stones. It is fairly soft (2.5–4), takes a bright polish, and can hold a static charge when rubbed. It is opaque with a waxy to glassy lustre on polished surfaces.

Where it is found

The most famous jet comes from Whitby, on the coast of Yorkshire in England, where it weathers from Jurassic shales. Whitby jet became hugely fashionable for Victorian mourning jewellery and remains the benchmark for the material.