sedimentary

Chert / Flint

Silicon Dioxide (SiO2)

Hardness: 7 (Mohs scale); Color: White, gray, or tan; Luster: Waxy to dull; Crystal structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Hardness: 7 (Mohs scale)
Color: White, gray, or tan
Luster: Waxy to dull

Identified July 18, 2026More sedimentary →

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Physical properties

Hardness: 7 (Mohs scale); Color: White, gray, or tan; Luster: Waxy to dull; Crystal structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Formation & geological history

Formed as nodules or beds in sedimentary rocks like limestone or chalk through the accumulation of silica-rich organic remains or chemical precipitation from groundwater. Most common in Paleozoic and Mesozoic strata.

Uses & applications

Historically used for stone tools (arrowheads, scrapers) and fire-starting. Currently used in road construction, stone jewelry (when colorful), and as a landscape material.

Geological facts

Flint is a variety of chert that occurs in chalk or marly limestone. It produces sparks when struck against steel, which made it vital for flintlock firearms and early survival tools.

Field identification & locations

Identify in the field by its very hard, smooth surface that cannot be scratched by a steel knife and its sharp, curved (conchoidal) edges when broken. Extremely common in riverbeds and limestone regions.