sedimentary

Chert (Flint)

Microcrystalline Quartz (SiO2)

Hardness: 7 Mohs; Color: Brown, grey, and white mottling; Luster: Waxy to dull; Crystal Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Hardness: 7 Mohs
Color: Brown, grey, and white mottling
Luster: Waxy to dull

Identified June 2, 2026More sedimentary →

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Physical properties

Hardness: 7 Mohs; Color: Brown, grey, and white mottling; Luster: Waxy to dull; Crystal Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Formation & geological history

Formed in marine environments through the accumulation of silica-rich organic remains or chemical precipitation within limestone or chalk beds. Most specimens date from the Phanerozoic eon.

Uses & applications

Historically used for stone tools and starting fires; currently used as a landscape stone, road aggregate, and for flint-knapping enthusiasts.

Geological facts

Flint was a vital resource for prehistoric humans to create sharp tools. When struck against steel, it creates sparks used to ignite gunpowder in flintlock firearms.

Field identification & locations

Identified by its extreme hardness, waxy appearance, and conchoidal (shell-like) fracture pattern. Commonly found as nodules in chalk or limestone outcrops and as water-worn pebbles in riverbeds.