sedimentary

Chert (flint), likely with iron-stained weathering rind

Microcrystalline quartz/chalcedony (SiO₂)

AI-generated identification · may be incorrect

Typically Mohs hardness 6.5–7, waxy to dull luster, conchoidal fracture, and no visible cleavage. This specimen is reddish-brown to gray-brown, with a smoother translucent brown fracture surface and a rough weathered exterior.

Identified August 10, 2026More sedimentary →

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Physical properties

Formation & geological history

Chert forms when silica-rich groundwater replaces or cements sediments, commonly as nodules in limestone or as bedded deposits. Its formation may range from Paleozoic to Cenozoic, depending on the host strata; the rusty color reflects iron oxides.

Uses & applications

Used historically for sharp tools and fire-starting, and occasionally as aggregate or decorative stone. Attractive polished pieces have modest collector value.

Geological facts

Fresh chert produces sharp, curved edges and can scratch glass; flint is generally the dark, high-quality variety of chert. The rough outer rind is consistent with weathering and iron staining.

Field identification & locations

Look for a very hard, compact stone, conchoidal breaks, and a dull or waxy surface; it should not fizz with dilute hydrochloric acid unless coated with limestone. Common worldwide, especially in limestone regions and river gravels.