sedimentary

Chert (Flint)

Chert (SiO2)

Hardness: 7 on Mohs scale; Color: Gray, tan, or brown; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7

Hardness: 7 on Mohs scale
Color: Gray, tan, or brown
Luster: Waxy to dull

Identified May 24, 2026More sedimentary →

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Physical properties

Hardness: 7 on Mohs scale; Color: Gray, tan, or brown; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7

Formation & geological history

Formed from the precipitation of silica-rich fluids or the accumulation of siliceous microfossils like diatoms or radiolaria in marine environments. Often found as nodules in limestone or chalk beds.

Uses & applications

Historically used for making stone tools (arrowheads, scrapers) and starting fires (flint and steel). Modern uses include road surfacing and some jewelry or lapidary work.

Geological facts

Flint is a variety of chert that occurs in chalk or marly limestone. It was the primary material for the Stone Age tool industry due to its ability to be knapped into sharp edges.

Field identification & locations

Identify in the field by its smooth, waxy surface and characteristic shell-like (conchoidal) curved fractures. It will easily scratch glass. Commonly found in riverbeds and areas with exposed limestone.