sedimentary

Likely flint (dark chert)

Microcrystalline quartz (SiO₂), commonly called chert or flint

AI-generated identification · may be incorrect

Dark brown to black, opaque, with a waxy-to-dull luster and irregular, shell-like conchoidal fractures; hardness about 7 Mohs. The image does not show crystal faces, and identification from appearance alone is uncertain.

Identified October 4, 2026More sedimentary →

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Physical properties

Formation & geological history

Forms when silica-rich material precipitates or replaces sediment in sedimentary rocks, often limestone or chalk. It occurs in rock layers and nodules; its age depends on the host formation.

Uses & applications

Historically used for tools and fire-starting; today it is mainly collected or used decoratively.

Geological facts

Sharp conchoidal edges made flint valuable for prehistoric cutting tools. The specimen appears to be a naturally fractured, unpolished piece.

Field identification & locations

Look for a hard, dense stone that scratches glass and breaks with curved, sharp-edged fractures; common in chalk and limestone regions worldwide. Similar-looking dark rocks can be distinguished more reliably with hardness and fracture tests.