sedimentary

Dark gray flint or chert fragment

Microcrystalline quartz (SiO₂), commonly with minor chalcedony and impurities

AI-generated identification · may be incorrect

Typically Mohs hardness 6.5–7, opaque dark gray to black, with a waxy-to-dull luster and no visible crystals or cleavage. It breaks with smooth, curved conchoidal fractures producing sharp edges.

Identified August 19, 2026More sedimentary →

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Physical properties

Typically Mohs hardness 6.5–7, opaque dark gray to black, with a waxy-to-dull luster and no visible crystals or cleavage. It breaks with smooth, curved conchoidal fractures producing sharp edges.

Formation & geological history

Chert forms when silica-rich groundwater replaces or fills sediment, often within limestone or chalk; its age depends on the host formation and may range from Paleozoic to Cenozoic. The specimen appears naturally fractured or possibly struck, exposing fresh surfaces.

Uses & applications

Historically used for stone tools and fire-starting; today it is mainly a teaching, collecting, and lapidary material, with limited aggregate use.

Geological facts

Flint is a variety of chert, commonly darkened by organic matter or iron/manganese impurities. Sharp conchoidal edges are a classic indicator of quartz-rich cryptocrystalline rock.

Field identification & locations

Look for glasslike conchoidal fracture, uniform fine texture, hardness sufficient to scratch glass, and lack of fizz in dilute hydrochloric acid. Common in limestone regions, including England, France, the Great Plains, and many sedimentary terrains.