sedimentary

Jet

Lignite (Anthracite-grade compact coal)

Hardness: 2.5–4.0 Mohs; Color: Velvety black or dark brown; Luster: Waxy to sub-metallic, takes high polish; Crystal Structure: Amorphous (non-crystalline); Specific Gravity: 1.30–1.35 (very lightweight/warm to touch)

Hardness: 2
Color: Velvety black or dark brown
Luster: Waxy to sub-metallic, takes high polish

Identified April 16, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed from the fossilized remains of wood (specifically the Araucariaceae family trees) buried under high pressure in anaerobic conditions within sedimentary layers. Most famous deposits are from the Toarcian age (Early Jurassic).

Uses & applications

Primarily used in jewelry making, ornamental carvings, and historical Victorian mourning jewelry. Due to its lightweight nature, it is well-suited for large beads/earrings.

Geological facts

Jet is a mineraloid, not a mineral. It was popularized by Queen Victoria, who wore it as mourning jewelry after Prince Albert's death. It is the origin of the phrase 'jet black'.

Field identification & locations

Identify by its weight (surprising light), 'warmth' to the touch compared to stone, and the 'hot needle test' (smells like burning coal). Often found on coastlines (like Whitby, UK) after storms wash away cliff faces.