sedimentary

Chert (Flint nodules in Limestone)

Silicon dioxide (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 on Mohs scale. Color: White, tan, or grey. Luster: Dull to waxy. Structure: Cryptocrystalline. Cleavage: None (conchoidal fracture). Specific gravity: 2.65.

Hardness: 7 on Mohs scale
Color: White, tan, or grey
Luster: Dull to waxy

Identified July 18, 2026More sedimentary →

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Physical properties

Hardness: 7 on Mohs scale. Color: White, tan, or grey. Luster: Dull to waxy. Structure: Cryptocrystalline. Cleavage: None (conchoidal fracture). Specific gravity: 2.65.

Formation & geological history

Formed through the replacement of calcium carbonate by silica in sedimentary marine environments, often as nodules or masses within limestone or chalk beds.

Uses & applications

Historically used for stone tools and starting fires; currently used as road aggregate, in landscaping, and as a raw material for ceramics.

Geological facts

Because it fractures conchoidally to create razor-sharp edges, chert was the primary material used by prehistoric humans for arrowheads, scrapers, and knives.

Field identification & locations

Can be identified in the field by its hardness (will scratch steel) and distinctive shell-like fracture pattern. Often found in outcrops where limestone has weathered away, leaving the harder chert exposed.