sedimentary

Chert (Polished/Tumbled)

Silicon Dioxide (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 Mohs; Color: Black with tan/brown bands; Luster: Waxy to vitreous; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); SG: 2.65

Hardness: 7 Mohs
Color: Black with tan/brown bands
Luster: Waxy to vitreous

Identified July 6, 2026More sedimentary →

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Physical properties

Hardness: 7 Mohs; Color: Black with tan/brown bands; Luster: Waxy to vitreous; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); SG: 2.65

Formation & geological history

Formed as a chemical precipitate or biochemical deposit in marine environments, where silica shells of organisms or dissolved silica accumulate and harden into rock over millions of years.

Uses & applications

Used for lapidary work (polishing, tumbling), jewelry accents, and historically for stone tools due to its sharp conchoidal fracture.

Geological facts

Chert that is darkly colored is often referred to as flint. This specific specimen shows characteristic bands of different mineral impurities, likely iron or organic matter, and has been tumbled to a smooth finish.

Field identification & locations

Identify in the field by its hardness (scratches glass), waxy feel, and smooth curved fractures. Commonly found in limestone or chalk beds and along riverbanks/beaches as rounded pebbles.