Jet

Jet, a compact lustrous variety of lignite (q.v.) resembling cannel coal, but harder and taking a better polish, f It is undoubtedly of organic origin, being generally, if not always, derived from coniferous wood. It burns with a thick smoke. It occurs in isolated masses in the bituminous shales in the zone of Ammonites' serpentinus, near the base of the Upper Lias at' Whitby in Yorkshire, where it was worked by the Romans, and seemingly even in the Bronze age. Its lightness renders it valuable for ornaments, and the tough Whitby jet can be readily carved. Jet is imitated by black glass and by ebonite.