Jet

Jet is an organic gem material, not a true mineral, formed from the fossilized wood of ancient trees that was compacted and chemically altered over millions of years. It is essentially a hard, gem-quality variety of lignite (brown coal).

Jet is prized for its deep, velvety black color, light weight, and ability to take a high polish. It is warm to the touch, unlike stone, and can be carved into intricate shapes. The most famous source is Whitby, on the coast of Yorkshire, England, where it became hugely popular for Victorian mourning jewelry.

Like amber, jet can become electrically charged when rubbed, which led both to be called by similar terms in antiquity.

Jet forms from waterlogged driftwood, often from monkey-puzzle-type (Araucaria) conifers, that sank into fine, oxygen-poor mud on ancient sea or lake floors. Buried and compressed by overlying sediment, the wood underwent gentle heat and pressure (coalification) that drove off volatiles and concentrated carbon, transforming it into a dense, fine-grained organic material.

Because it forms from individual logs in marine shales, jet occurs as isolated lenses and seams rather than thick coal beds. The classic Whitby jet comes from Lower Jurassic shales of the Yorkshire coast; other deposits occur in Spain, the USA (Utah, Colorado), Germany, and Poland.

Look for a lightweight, opaque, deep black material that is warm to the touch, takes a high glassy-to-resinous polish, and has a hardness of only about 2.5-4, so it can be scratched by a coin.

Jet has a brown streak and, when tested on an unglazed porcelain tile, leaves a chocolate-brown to black streak (unlike harder black stones). It is also notably light and slightly warm compared with glass or stone imitations.

Look-alikes include black glass ("French jet," heavier, cold, conchoidal fracture), black onyx (much harder, cold, denser), vulcanite and bakelite (plastics, may smell when heated), and anthracite coal (more brittle). The warmth, light weight, low hardness, and brown streak identify true jet.

Jet has been used since prehistoric times for beads, amulets, and ornaments, but is most famous for Victorian mourning jewelry, popularized after Queen Victoria wore Whitby jet following Prince Albert's death. It is carved into beads, cameos, brooches, rosaries, and pendants.

Because it is soft and lightweight, it is ideal for detailed carving but requires careful wear to avoid scratches. Antique Whitby jet pieces are collectible and can be valuable.

In the metaphysical market jet is marketed as a protective, grounding stone for absorbing negative energy and supporting grief, though these claims are not scientific. Its main value today is historical, ornamental, and collectible.