sedimentary

Flint (gray chert)

Microcrystalline quartz (SiO₂), a variety of chert

AI-generated identification · may be incorrect

Hardness about 7 Mohs; gray to brown with a waxy or dull luster, no visible crystals or cleavage, and a conchoidal fracture with sharp edges. The specimen appears to be a natural, roughly knapped flint nodule.

Identified October 4, 2026More sedimentary →

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Physical properties

Formation & geological history

Forms when silica-rich fluids replace or fill sediment in marine limestone and chalk; such deposits occur across many geological ages, especially the Cretaceous. Its exact age and source cannot be determined from the image.

Uses & applications

Historically used for tools, arrowheads, and fire-starting; today collected and sometimes used in decorative work.

Geological facts

Flint’s sharp conchoidal fracture made it valuable for prehistoric cutting tools and later flintlock firearms.

Field identification & locations

Look for dense, fine-grained material that scratches glass and breaks into curved, sharp-edged surfaces; common in chalk and limestone regions. Image-only identification is approximate.