sedimentary

Chert (Iron-Stained)

Microcrystalline Silica (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 (Mohs scale), Color: Tan to yellowish-brown due to iron staining, Luster: Waxy to dull, Crystal structure: Cryptocrystalline, Cleavage: None (conchoidal fracture), Specific gravity: 2.65

Identified March 25, 2026More sedimentary →

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Physical properties

Hardness: 7 (Mohs scale), Color: Tan to yellowish-brown due to iron staining, Luster: Waxy to dull, Crystal structure: Cryptocrystalline, Cleavage: None (conchoidal fracture), Specific gravity: 2.65

Formation & geological history

Formed through the accumulation of silica-rich microfossils or precipitation from hydrothermal fluids within sedimentary rock layers. Its rounded shape suggests it was weathered out from a host rock like limestone and tumbled in a stream or river bed.

Uses & applications

Historically used for stone tools and arrowheads. Currently used as construction aggregate, road base, and occasionally as a tumbling stone for lapidary enthusiasts.

Geological facts

Chert is so hard that it can strike sparks against steel, a property used by ancient people to start fires. Variations including jasper, flint, and agate are all members of the chalcedony/chert family.

Field identification & locations

Identify in the field by its hardness (it can scratch glass), its smooth 'river-rock' texture, and its shell-like (conchoidal) fracture if broken. Commonly found in riverbeds and areas with exposed limestone or chalk.