sedimentary

Chert with Weathered Rind (Flint/Chalcedony)

Microcrystalline Quartz (SiO2)

Hardness: 7 on Mohs scale. Color: Grayish interior with yellowish-tan weathered outer cortex or rind. Luster: Waxy to dull. Fracture: Conchoidal with sharp edges. Structure: Cryptocrystalline/microcrystalline.

Hardness: 7 on Mohs scale
Luster: Waxy to dull

Identified July 25, 2026More sedimentary →

Explore Chert with Weathered Rind (Flint/Chalcedony) in the encyclopedia →

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Physical properties

Formation & geological history

Formed via the precipitation of silica in marine environments, often replacing organic carbonate material or accreting in nodular form within limestone or chalk formations. The exterior displays a distinct weathered oxidation rind.

Uses & applications

Historically used for stone tools, flintknapping, and starting fires. Modern use is primarily for road aggregate, lapidary projects, and casual mineral collecting.

Geological facts

Chert and flint are among the oldest materials used by humans to craft tools due to their predictable conchoidal fracture and extremely sharp freshly broken edges.

Field identification & locations

Identified by its high hardness (scratches glass), smooth waxy texture, shell-like conchoidal fracture on the grey inner face, and a distinct tan/yellow chalky or oxidized outer crust. Commonly found in riverbeds, gravel pits, and limestone outcrops worldwide.

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