sedimentary

Chert or flint fragment

Microcrystalline quartz (SiO₂), likely iron-stained chert

AI-generated identification · may be incorrect

Typically Mohs hardness 6.5–7, waxy to dull luster, brown-gray coloration, and no visible cleavage; the specimen shows a smooth, fine-grained texture, translucent edges, and rusty iron-oxide staining. Its shape appears naturally water-worn, possibly with a sharper fractured edge.

Identified August 10, 2026More sedimentary →

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Physical properties

Formation & geological history

Chert forms when silica from microscopic organisms or groundwater replaces sediment, commonly in limestone or chalk, during diagenesis; its age depends on the host formation and cannot be determined from the image. The rounded surface suggests transport in a stream, beach, or glacial deposit.

Uses & applications

Used historically for sharp tools and fire-starting because it fractures conchoidally; today it is mainly a lapidary, teaching, or small collecting material. It has little commercial value unless unusually patterned or gem-quality.

Geological facts

Flint is a dark, dense variety of chert, while “chert” is the broader geological term. Conchoidal fracture and translucent margins are key diagnostic features.

Field identification & locations

Look for a glassy or waxy surface, very fine grain, conchoidal fractures, and inability to scratch it with a steel knife; it should scratch ordinary glass. Common in sedimentary regions worldwide, especially limestone and chalk terrains.