Jet Identification Guide

What Jet Looks Like

Jet is a gem-quality variety of lignite — fossilized wood compressed and altered over millions of years. It is a deep, velvety black organic 'mineraloid,' very light in weight, and takes a high polish prized for Victorian mourning jewelry.

• Color: uniform deep black (sometimes very dark brown)
• Luster: velvety, waxy to glassy when polished
• Transparency: opaque
• Form: massive, often retaining woody/grain texture; no crystals (organic)

Step-by-Step Field-ID Checklist

1. Heft it — it's very light. Jet feels warm and feather-light, unlike cold, heavy glass or stone.
2. Streak test. Rub on unglazed porcelain: jet leaves a brown to dark-brown streak (key diagnostic). Black glass and onyx leave white/no streak.
3. Feel the warmth. Like amber, jet is a poor heat conductor and feels warm to the touch, not cold like glass.
4. Hot-point or static test (cautiously): rubbing jet builds a static charge that picks up small paper bits (like amber); a heated point gives a coal-like, sooty smell. These are destructive—use only on scrap.
5. Check hardness: soft, Mohs 2.5–4; can be scratched with a knife.

Key Diagnostic Tests

• Mohs hardness: 2.5–4 (soft)
• Streak: brown to chocolate-brown — diagnostic
• Specific gravity: ~1.1–1.4 — extremely low; floats or barely sinks, unlike glass/onyx
• Fracture: conchoidal
• Warm feel; develops static charge when rubbed
• Burns with a coal-like smell (destructive test only)

Common Look-Alikes and How to Tell Them Apart

• Black glass ('French jet'): cold to the touch, much denser/heavier, white streak, harder (5.5), and may show mold bubbles. Jet is warm, light, and streaks brown.
• Black onyx/chalcedony: much harder (7), denser, cold, white streak; will not take a static charge.
• Vulcanite/ebonite (hardened rubber) and Bakelite: vulcanite fades to khaki-brown and smells of rubber when warmed; Bakelite smells of carbolic/formaldehyde and is denser.
• Black tourmaline/obsidian: harder, denser, cold, and not organic; obsidian has conchoidal glassy fracture and white streak.
• Anthracite coal: brighter, more brittle, and not as tough or polishable as gem jet.

Where Jet Is Found

The classic source is Whitby, North Yorkshire, England (Jurassic shales), the heart of the Victorian jet trade. Other deposits occur in Spain (Asturias), the USA (Utah, Colorado, New Mexico), Poland, and Russia. Jet is found in carbonaceous shales and coal-bearing sediments, sometimes washed onto beaches.