Jet
Jet fossilised wood including Whitby jet, properties, Victorian significance, identification, and distinguishing from simulants.
Introduction
Jet is a compact form of lignite coal derived from fossilised driftwood, most commonly
Araucaria-type conifers buried in anaerobic marine or freshwater sediment, and is an
organic gem with no crystal system. The Whitby, Yorkshire deposits are Jurassic in age
(approximately 180 million years) and produce hard jet formed under marine conditions;
freshwater-derived soft jet is more brittle and less valuable. [1] Diagnostic
properties: hardness 2.5–4 Mohs, SG 1.30–1.35 (very light), spot RI approximately 1.66,
and a bituminous coal-like smell on the hot-needle test. These values immediately separate
genuine jet from black glass ("French jet", SG 2.3–2.5, cold, no smell), vulcanite rubber
(SG ~1.1, sulphurous smell), and black onyx (SG 2.65, Mohs 7). Jet's extreme lightness
suits large carved pieces that would be heavy in glass. After Prince Albert's death in
1861, Queen Victoria adopted Whitby jet as the standard mourning gem, driving an industry
that employed over 1,400 Whitby workers at its 1870s peak.
Formation and Composition
How jet forms:
Formation Process
- Wood (often Araucaria trees) falls into water
- Becomes waterlogged and sinks into sediment
- Anaerobic conditions prevent complete decay
- Heat and pressure over millions of years
- Carbon-rich compact material forms
Composition
- Origin: Fossilised driftwood
- Type: Compact lignite coal
- Age: Jurassic period (~180 million years for Whitby) [1]
- Carbon content: High (similar to coal)
Physical Properties [1]
| Property | Value |
|---|---|
| Hardness | 2.5–4 Mohs |
| Specific gravity | 1.30–1.35 (very light) |
| Refractive index | 1.66 (spot; often difficult) |
| Lustre | Waxy to vitreous when polished |
| Colour | Black (brown in thin sections) |
| Fracture | Conchoidal |
Types of Jet
Jet quality varies by source:
Hard Jet
- Forms in saltwater (marine) conditions
- More compact and durable
- Takes better polish
- Higher value
- Whitby jet is this type
Soft Jet
- Forms in freshwater conditions
- Less durable
- May crack over time
- Lower value
- More common
Whitby Jet
Victorian Mourning Jewellery
Jet's historical significance:
The Victorian Era
- Prince Albert died in 1861
- Queen Victoria wore jet mourning jewellery
- Fashion followed the Queen's example
- Whitby jet industry boomed 1860s–1880s
- Over 1,400 jet workers in Whitby at peak [CITATION NEEDED]
Mourning Jewellery Types
- Brooches and pendants
- Necklaces and bracelets
- Carved cameos and intaglios
- Crosses and religious items
- Hair jewellery with jet components
Identification
Distinguishing jet from simulants:
| Material | SG | Feel | Test |
|---|---|---|---|
| Jet | 1.30–1.35 | Warm; light | Coal smell when heated |
| Black glass (French jet) | 2.3–2.5 | Cold; heavy | No smell; may show bubbles |
| Vulcanite (hard rubber) | 1.1–1.2 | Rubbery; very light | Rubbery/sulphur smell |
| Bakelite | 1.25–1.35 | Plastic feel | Carbolic acid smell |
| Black onyx | 2.65 | Cold; heavy | Much harder (H 7) |
| Bog oak | ~1.2 | Woody grain | Wood smell; shows grain |
Hot Needle Test
Care and Durability
Jet care considerations:
Advantages
- Warmer to touch than glass simulants
- Lightweight for large pieces
- Takes excellent polish
- Relatively durable for organic gem
Care Guidelines
- Store separately from harder gems
- Clean with damp cloth
- Avoid harsh chemicals
- Polish gently if needed
- Avoid extreme heat or dryness
- Can crack if dried out (especially soft jet)
Market Considerations
Jet market factors:
- Antique value: Victorian pieces collectible
- Whitby premium: Genuine Whitby commands higher prices
- Modern production: Limited Whitby; Spanish jet available
- Simulants common: Much "jet" is glass or plastic
- Provenance important: Documentation adds value
References
- ↑ 1. Read, P. (2008). Gemmology (3rd ed.). Butterworth-Heinemann. ISBN: 978-0-7506-6449-3. DOI: 10.4324/9780080507224.