sedimentary

Gray-green flint/chert fragment

Microcrystalline quartz (SiO₂), likely chert or chalcedony-rich material

AI-generated identification · may be incorrect

Hardness about 6.5–7 Mohs; opaque gray-green color, dull to waxy luster, very fine-grained cryptocrystalline structure, and conchoidal-looking fracture. The pale edge may reflect weathering or a silica-rich cortex.

Identified September 13, 2026More sedimentary →

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Physical properties

Formation & geological history

Chert forms when dissolved silica replaces or fills pores in limestone and other sediments, commonly during the Paleozoic–Cenozoic; its exact age cannot be determined from the image. This piece appears naturally weathered or possibly struck, producing sharp flake-like margins.

Uses & applications

Used historically for cutting tools, arrowheads, fire-starting, and aggregate; attractive polished pieces may be sold as lapidary material. Common specimens generally have modest value.

Geological facts

Chert can resemble glassy volcanic rock, but its uniformly dull, waxy surface and predictable conchoidal fracture are characteristic. A steel file should barely scratch it, while quartz should not.

Field identification & locations

Common in limestone regions, river gravels, glacial deposits, and archaeological sites worldwide; examine for hidden cortex, banding, fossils, or deliberate flake scars. Identification would be improved by a scratch test and specific-gravity test.