sedimentary

Chert (Flint)

Chert (SiO2)

Hardness: 7 (Mohs); Color: Dark grey to black; Luster: Dull to waxy; Crystal Structure: Microcrystalline (Cryptocrystalline) Quartz; Cleavage: None (Conchoidal fracture); Specific Gravity: 2.65

Hardness: 7 (Mohs)
Color: Dark grey to black
Luster: Dull to waxy

Identified June 22, 2026More sedimentary →

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Physical properties

Hardness: 7 (Mohs); Color: Dark grey to black; Luster: Dull to waxy; Crystal Structure: Microcrystalline (Cryptocrystalline) Quartz; Cleavage: None (Conchoidal fracture); Specific Gravity: 2.65

Formation & geological history

Formed in sedimentary environments via the accumulation of siliceous remains of organisms (like diatoms) or chemical precipitation. It often occurs as nodules in limestone or chalk beds. Most specimens date from various geological periods, often Cretaceous.

Uses & applications

Historically used for making stone tools (arrowheads, scrapers) due to its sharp edges when fractured. Also used as a spark striker in flintlock firearms and primitive fire-starting. Occasionally used as decorative stones or in heavy construction flint-knapping.

Geological facts

Flint is a variety of chert. It was one of the most important minerals for early humans, essentially defining the 'Stone Age.' When struck against steel, it creates sparks that can start fires.

Field identification & locations

Identify by its characteristic oyster-shell-like (conchoidal) fracture pattern and its ability to scratch glass. Commonly found in chalk or limestone outcrops, or as pebbles in riverbeds and on beaches. Collectors look for unique colors or worked edges.