sedimentary

Chert (flint)

Microcrystalline quartz (SiO₂), commonly called chert; flint is a dark variety

AI-generated identification · may be incorrect

Hardness about 7 Mohs; gray-brown, waxy to dull luster, very fine-grained with no visible crystals or cleavage. The sharp, curved fracture surfaces are characteristic of conchoidal fracture.

Identified October 4, 2026More sedimentary →

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Physical properties

Hardness about 7 Mohs; gray-brown, waxy to dull luster, very fine-grained with no visible crystals or cleavage. The sharp, curved fracture surfaces are characteristic of conchoidal fracture.

Formation & geological history

Forms when silica accumulates and recrystallizes in sedimentary rocks, often replacing limestone or precipitating from marine sediments. The specimen’s age and precise origin cannot be determined from the image.

Uses & applications

Historically used for cutting tools and fire-starting; today used for knapped artifacts, decorative pieces, and collecting.

Geological facts

Chert can be chipped into exceptionally sharp edges; its fracture was widely exploited by prehistoric people.

Field identification & locations

Look for a dense, hard, fine-grained piece with conchoidal fractures and edges that can scratch glass. Chert occurs worldwide, especially in limestone and chalk regions.