sedimentary

Brown chert or flint fragment

Microcrystalline quartz (SiO₂), commonly termed chert; exact identification requires testing

AI-generated identification · may be incorrect

Hardness about 6.5–7 Mohs; opaque reddish-brown to dark brown, waxy-to-dull luster, very fine-grained cryptocrystalline structure, and conchoidal fracture. The pale lines may be veins, weathering cracks, or silica-rich bands.

Identified September 13, 2026More sedimentary →

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Physical properties

Formation & geological history

Forms when silica-rich groundwater replaces or fills pore spaces in limestone, chalk, or marine sediments, often during diagenesis. Chert ranges from Precambrian to modern geological ages and is widespread in sedimentary terrains.

Uses & applications

Historically used for sharp-edged tools, fire-starting, and arrowheads; attractive pieces are collected or used in lapidary work, though this fragment appears unpolished and ordinary.

Geological facts

Its fracture can produce extremely sharp edges, making chert crucial to prehistoric toolmaking. Red-brown coloration commonly reflects iron oxides or hydroxides.

Field identification & locations

Look for a glassy or waxy surface, conchoidal fracture, no visible grains, and inability to scratch it with a steel knife; it should scratch ordinary glass. Common in limestone and chalk regions worldwide; acid fizzing would suggest attached calcite rather than the chert itself.