sedimentary

Chert (likely brown flint)

Microcrystalline quartz, SiO₂ (chalcedonic quartz aggregate)

AI-generated identification · may be incorrect

Hardness 6.5–7; dark brown to reddish-brown, opaque, and typically dull to waxy with a conchoidal fracture. Very fine-grained, compact, and lacks visible cleavage; specific gravity is about 2.6.

Identified August 15, 2026More sedimentary →

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Physical properties

Hardness 6.5–7; dark brown to reddish-brown, opaque, and typically dull to waxy with a conchoidal fracture. Very fine-grained, compact, and lacks visible cleavage; specific gravity is about 2.6.

Formation & geological history

Forms when silica-rich groundwater replaces or precipitates within carbonate sediments, commonly from biogenic silica. Most specimens are Paleozoic to Cenozoic, though chert occurs throughout geological time.

Uses & applications

Used historically for cutting tools and fire-starting, and today as aggregate, road material, and a collector specimen. Attractive varieties may be polished for decorative objects.

Geological facts

The sharp, curved fracture surfaces can produce extremely keen edges. Brown coloration commonly reflects iron oxides or organic matter.

Field identification & locations

Identify by its glassy-to-waxy appearance, very hard scratch resistance, and conchoidal fracture; it should scratch glass. Common in limestone and chalk regions worldwide, including England, Texas, Kansas, and the Great Lakes region.