sedimentary

Brown chert (likely flint)

Microcrystalline quartz (SiO₂), variety chert; identification from the image is approximate

AI-generated identification · may be incorrect

Opaque brown, waxy to dull luster, with sharp conchoidal fracture and no visible crystals or cleavage. Mohs hardness about 7; specific gravity about 2.6.

Identified October 10, 2026More sedimentary →

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Physical properties

Opaque brown, waxy to dull luster, with sharp conchoidal fracture and no visible crystals or cleavage. Mohs hardness about 7; specific gravity about 2.6.

Formation & geological history

Forms when silica-rich material precipitates or replaces sediment, commonly in limestone or chalk. Chert occurs in rocks of many geological ages.

Uses & applications

Used historically for tools and fire-starting; today it is mainly a collecting specimen or source of knappable material.

Geological facts

Its curved, shell-like fracture can produce very sharp edges, making chert important in prehistoric toolmaking.

Field identification & locations

Look for hardness near 7, a smooth fracture surface, and no fizz in dilute acid. Chert is widespread; a small common fragment like this is typically worth about $1–$10.