sedimentary

Tumbled brown chert or flint

Microcrystalline quartz (SiO₂), commonly with chalcedony

AI-generated identification · may be incorrect

Hardness about 6.5–7 Mohs; opaque tan to brown, waxy to dull luster, very fine-grained and massive, with no visible cleavage. The smoothly rounded surface indicates natural water abrasion or tumbling; faint lighter patches may be weathering or included silica.

Identified September 14, 2026More sedimentary →

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Physical properties

Formation & geological history

Chert forms when silica-rich groundwater or marine silica replaces carbonate sediment or accumulates as siliceous ooze, generally during sedimentary burial. Its exact geological age cannot be determined from the photograph; chert ranges from Precambrian to modern formations.

Uses & applications

Used historically for sharp tools and fire-starting because it fractures conchoidally; today it is mainly a landscaping, lapidary, and collecting material.

Geological facts

Chert and flint are mineralogically similar; “flint” usually refers to dark, nodular chert associated with chalk. The specimen’s shape and polish obscure diagnostic fracture surfaces.

Field identification & locations

Look for a glassy or waxy texture, conchoidal fracture, and inability to scratch it with a steel knife; quartz-rich chert can scratch glass. Common in limestone and chalk regions, including the Midwest, Texas, England, and France.