sedimentary

Likely brown chert (flint) fragment

Microcrystalline quartz (SiO₂), commonly called chert

AI-generated identification · may be incorrect

Opaque brown-gray, dull to slightly waxy surface; chert has Mohs hardness about 7 and no cleavage, with a conchoidal fracture. The image alone does not show enough detail for a definitive identification.

Identified October 4, 2026More sedimentary →

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Physical properties

Formation & geological history

Chert forms when silica precipitates or replaces sediment, often in limestone or marine deposits; its age depends on the host formation and cannot be determined from the specimen.

Uses & applications

Chert has historically been used for cutting tools and fire-starting; attractive pieces are collected, though this fragment appears unworked.

Geological facts

A sharp, curved, shell-like fracture and ability to scratch glass are useful clues for chert.

Field identification & locations

Common worldwide in sedimentary rocks and gravel. Check for a glass-scratching edge and conchoidal fracture; brown coloration may come from iron impurities.