The making of jet or mourning jewelry was once a very large industry in France and England, and even now Whitby jet is well known in commerce.

Jet is a species of bituminous coal (cannel coal) which can be cut with a knife. The hardness is 1 to 2.5; specific gravity, 1.35; its lustre is not very high, and color pitch-black.

It is found in England, France, Hesse, Spain, Italy, and Prussia.