sedimentary

Dark flint or chert nodule

Microcrystalline quartz (SiO₂), commonly called flint when dark and nodular

AI-generated identification · may be incorrect

Identified August 16, 2026More sedimentary →

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Physical properties

Hardness about 6.5–7 Mohs; charcoal-gray to black, dull to waxy or slightly vitreous luster, very fine-grained cryptocrystalline structure, no visible cleavage, conchoidal fracture, and typical specific gravity near 2.6. The rounded, irregular form and subtly lighter weathered areas are consistent with a natural nodule.

Formation & geological history

Forms when silica replaces or fills cavities in marine limestone or chalk, often during early diagenesis. It can range from Paleozoic to Cenozoic in age; the image alone cannot determine its age or locality.

Uses & applications

Used historically for stone tools, fire-starting and knappable edges, and occasionally as aggregate or ornamental stone. Common pieces have little commercial value unless unusually patterned, colorful, or historically significant.

Geological facts

Flint is a variety of chert distinguished mainly by its dark color and common association with chalk. Freshly fractured surfaces are typically sharp-edged and glass-like.

Field identification & locations

Common in limestone and chalk regions, including England, France, Denmark, the Great Lakes, and many sedimentary terrains worldwide. Test cautiously with a steel file or glass: it should scratch glass and produce a conchoidal break; acid typically causes no reaction.