sedimentary

Weathered flint or chert nodule

Microcrystalline quartz (SiO₂), commonly flint/chert

AI-generated identification · may be incorrect

Hardness about 6.5–7 Mohs; gray, cream, and ochre-brown coloration with a dull to waxy luster, irregular conchoidal fracture, and no visible cleavage. The brown areas likely reflect iron-oxide staining or weathering.

Identified September 21, 2026More sedimentary →

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Physical properties

Formation & geological history

Forms when silica-rich groundwater replaces or fills cavities in limestone, often during the Cretaceous or other Phanerozoic sedimentary periods. The rounded surface and discoloration indicate weathering from its host rock.

Uses & applications

Historically used for sharp-edged tools, fire-starting, and arrowheads; today it is mainly a teaching or lapidary material. Attractive pieces may be polished for display.

Geological facts

Fresh broken surfaces are typically glassy and sharp, while weathered rinds can be porous or chalky. It may contain fossils or relic textures from the original limestone environment.

Field identification & locations

Common in limestone regions, including parts of England, France, the American Midwest, and Texas. A steel file usually scratches it only with difficulty; streak is generally white, and it does not effervesce strongly in dilute hydrochloric acid.