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.
Physical & Optical Properties
RI Range1.640–1.680
SG Range1.10–1.40
SG Typical1.32
Hardness (Mohs)2.5–4
Crystal SystemAmorphous
Optic CharacterSR (Singly Refractive)
Dispersion0.000
Fluorescence LWInert
Fluorescence SWInert
Chelsea FilterNot Applicable
PleochroismNone
ColorsBlack
SpeciesOrganic Mineraloid (compact lignite)
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
Natural — low ($/ct)$20
Natural — high ($/ct)$200
NotePer carat for cut material; antique Victorian Whitby jet pieces command $50–500+ per item; Spanish jet (softer, 'soft jet') is less valued than Whitby (hard jet)
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.
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