Key properties
| Chemical formula | Organic: primarily C with H and O (fossilised conifer wood, Araucariaceae) |
| Crystal system | Amorphous (none — organic) |
| Mohs hardness | 2.5-4 |
| Toughness | Poor to fair (brittle, cracks with rough wear) |
| Refractive index | 1.640-1.680 |
| Optic character | Isotropic (SR) — single spot reading about 1.66 |
| Specific gravity | 1.30-1.34 |
| Cleavage | None |
| Fracture | Conchoidal to uneven |
| Habit | Nodules, rods and seams of compact fossil wood; sometimes preserving woody grain textures |
| Lustre | Dull to greasy on broken surfaces; polish: Resinous to vitreous, warm satin-like |
| UV fluorescence | Inert |
| Pleochroism | None |
| Cause of colour | Deep black from carbon-rich fossilised plant tissue; brown tone visible in thin edges and streak |
| Typical inclusions | Preserved wood grain, pyrite inclusions, occasional cracks; thin splinters show dark brown in transmitted light |
| Stability | Burns readily with a sooty, coal-like odour; stable to light; acids may dull the polish; cracks if overheated or dried rapidly |
| Heat sensitivity | Extreme — a hot point produces coal smoke; never steam or ultrasonic |
| Care and cleaning | Dry or barely damp soft cloth; if needed brief cool soapy water and immediate gentle drying; never ultrasonic, steam, hot water, solvents or perfume |
| Birthstones | None (traditional Victorian mourning jewellery material) |
| Availability | Limited — genuine Whitby jet commands collector prices; Spanish and other jet is available in smaller volume |
| Recognition | Light in the hand (SG ~1.32), warm to the touch, takes static electricity when rubbed with wool, brown streak, hot point smells of coal; spot RI 1.66 |
Varieties
Jet
| Colour | velvet black, brown in strong transmitted light |
| Transparency | opaque |
| Clarity type | Not applicable — opaque |
| Phenomena | None |
| Appearance | Deep uniform black that takes a soft resinous-vitreous polish, noticeably lighter and warmer than any black mineral or glass; carved beads, chains and cameos show crisp detail |
| Trade names | Whitby jet (the quality benchmark) • hard jet • Oltu stone (Turkey, Erzurum area) |
| Misnomers | Black amber (a folk name — jet is not resin) • Paris jet (actually black glass) • French jet (black glass) |
| Typical sizes | Beads 4-20 mm; carved pendants, brooches and chains from a few carats to statement pieces; large antique necklaces survive whole |
| Cutting styles | Beads • carved chains and links • cameos and intaglios • cabochons • tumbled pieces |
| Key separations | vs black glass ('French jet'): glass is cold and heavy (SG ~2.4-2.6), vitreous, conchoidal glossy chips; jet warm, light (1.32) • vs vulcanite/ebonite (hard rubber): rubber smells of sulfur/burnt rubber under hot point and shows moulded seams; jet smells of coal • vs black chalcedony/onyx: onyx hard (7), cold, RI 1.54, SG 2.6 • vs obsidian: glassy lustre, SG ~2.4 • vs black coral: coral shows concentric growth rings and granular fracture; jet is structureless • hot point (on a hidden spot or shaving): jet = coal odour, shaving breaks rather than curls |
| Sources (localities) | England (Whitby, North Yorkshire — classic hard jet of the Jurassic 'Jet Rock') • Spain (Asturias — main modern European supply) • USA (New Mexico Acoma district; Colorado; Utah) • Turkey (Erzurum — Oltu stone) • France (Aude) • Poland (Wadowice area) |
| Availability | Limited; Whitby material scarce and collectable, Spanish and Turkish jet fills lower price tiers |
| Market notes | Antique Victorian Whitby jet auctions well above modern material; much 'jet' sold to tourists is actually glass, plastic or vulcanite — always test |
| Care notes | Last piece on, first off; keep from perfume, hairspray, heat and prolonged water; store wrapped and dry; ultrasonic and steam will destroy it |
| In short | Jet is the Victorian mourning classic — warm, light, black as velvet and unmistakable once hefted. Genuine Whitby pieces are antiques with a following; everything else black on the market must be separated by weight, feel and the hot point. |
| Size (ct) | USD per carat | Tier | As of |
|---|---|---|---|
| 1.00–20.00 | $1.00 – $8.00 | modern carved beads and cabs (Spanish/Turkish) | 2026-10-26 |
| 1.00–50.00 | $10.00 – $60.00 | genuine Whitby jet and Victorian antique | 2026-10-26 |
Retail market survey, per carat unless noted. Ranges describe what commercial to fine stones trade at; exceptional stones and provenance premiums sit above them.
Sources
GIA gem encyclopedia · mindat.org · Wikipedia
Data compiled and fact-checked against gemmological literature, October 2026 (JDMIS gem reference). Properties are ranges accepted in gemmological practice; individual stones vary.
See also
Gemstone reference entries: gem #221
Related materials: Corundum · Diamond · Opal · Quartz · Spinel · Topaz
Identification wizard · All 83 materials · Singapore gem labs