Jet
Last updated: April 2026
Organic gemstone formed from compacted driftwood (Araucaria trees) buried and transformed over geologic time — a very compact lignite coal. Whitby, Yorkshire is the primary source. Key field tests: warm to touch, very low SG (~1.3), develops static electricity when rubbed.
Jet has a specific gravity of 1.32 and a refractive index of 1.640–1.680, with a Mohs hardness of 2.5–4.0. It is singly refractive.
Physical & Optical Properties
Key Differentiators
- Extremely low SG 1.10–1.40 — nearly floats in saturated salt water; noticeably light in hand
- Warm to touch — organic material has low thermal conductivity unlike glass or onyx
- Static electricity effect — brisk rubbing on wool attracts small pieces of paper or light debris
- Brown streak on unglazed porcelain — distinguishes from black glass (no streak) and onyx (white streak)
- Hot needle produces distinctive coal/burning wood smell — not sulfur (vulcanite) or plastic
Common Simulants
- Black Glass (French Jet): Black glass SG 2.4+; cold to touch; no streak on porcelain; no static electricity effect; no burning smell with hot needle.
- Black Onyx: Black onyx (chalcedony) SG ~2.6; cold to touch; white streak; no static; no burning smell. Much harder (H 7).
- Vulcanite (Hard Rubber / Ebonite): Victorian simulant — SG ~1.15 (may float); sulfur smell on hot needle; tends to turn brown/khaki with age unlike jet.
- Black Plastic: Modern simulant — acrid plastic smell on hot needle; SG varies; no streak; may feel lighter and look too perfect under loupe.
- Black Tourmaline (Schorl): Tourmaline SG 3.0–3.26; hard (H 7–7.5); vitreous luster but clearly heavier than jet; no static effect.
Treatments
- Wax Polishing (surface sheen enhancement)
Price Context
Price context is approximate. GemID is not an appraisal tool. Results are indicators, not certified valuations.
Measurement Guides
Identifying a jet? GemID walks through these tests in order — RI, SG, fluorescence, and more.
Try GemID Free →Studying for the GIA, FGA, or FEEG practical? Jet is one of the 130 species in GemID’s drill and exam pool — practice identifying it from its measured properties under timed exam conditions.
Practice exams →