sedimentary

Possible flint or black chert

Microcrystalline quartz (SiO₂), likely chert/flint

AI-generated identification · may be incorrect

Typically Mohs hardness 6.5–7, opaque black to dark gray, with dull to waxy luster and no visible crystals or cleavage; conchoidal fracture produces sharp edges. The specimen appears naturally dark and roughly worked or fractured, but image-only identification is tentative.

Identified September 19, 2026More sedimentary →

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Physical properties

Formation & geological history

Chert forms when silica-rich groundwater replaces or fills sediment, commonly in limestone; flint is a dark variety associated especially with chalk. It may range from Paleozoic to Cenozoic in age, depending on its host formation.

Uses & applications

Used historically for tools, arrowheads, fire-starting, and knapping; attractive polished pieces are sold as lapidary material. Common specimens usually have modest value.

Geological facts

A fresh fracture can reveal a smoother, glasslike surface and razor-sharp edge. Black color may result from organic matter, iron, or manganese impurities.

Field identification & locations

Look for very fine grain, waxy feel, conchoidal fracture, and inability to scratch it with a steel knife; it should scratch glass. Common worldwide in limestone and chalk regions.