Jet

Jet is fossilized wood - specifically, the remains of Araucaria-type coniferous trees that fell into anoxic (oxygen-free) swamp or marine environments during the Jurassic period, roughly 180 million years ago. Under pressure and in the absence of oxygen, the wood underwent a process similar to coal formation but retained more of its original cellular structure.

Jet from Whitby, England, formed from trees that fell into a Jurassic sea and were buried in marine shale. This distinguishes it from 'hard jet' that formed in freshwater environments - the marine Whitby jet is denser and takes a better polish. Whitby has been the world's premier jet source since the Bronze Age.

Jet is extremely lightweight (SG 1.30 - it barely sinks in water), warm to the touch, and generates static electricity when rubbed - properties it shares with amber, another organic gem. Despite being millions of years old, jet retains enough volatile compounds to burn with a smoky flame, which was used historically as an identification test.

Jet is identified by its intense black color, very low density (feels surprisingly light), warmth to the touch, and ability to generate static charge when rubbed on fabric. The streak is dark brown, not black.

Distinguish from obsidian (much denser, glassy fracture, cold to touch), black onyx (much denser, harder), black tourmaline (crystal faces, much denser), and glass (cold, denser). Jet's extreme lightness is its most practical diagnostic - if a black material feels unexpectedly light, it's likely jet or plastic.