sedimentary

Chert (Iron-stained)

Silicon Dioxide (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 on Mohs scale; Color: Tan to reddish-brown due to iron oxide staining; Luster: Waxy to dull; Structure: Cryptocrystalline (microscopic quartz); Cleavage: None, exhibits conchoidal fracture.

Hardness: 7 on Mohs scale
Color: Tan to reddish-brown due to iron oxide staining
Luster: Waxy to dull

Identified July 16, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed as a chemical precipitate or biochemical deposit in marine environments where silica-rich fluids replace organic material or accumulate as ooze. This specimen shows river-worn tumbling and oxidation weathering.

Uses & applications

Historically used for making stone tools (arrowheads) due to its sharp edges when broken. Today used in construction aggregate and as road surfacing material in some regions.

Geological facts

Chert is so durable that it often remains behind as gravel after the surrounding softer rocks like limestone have eroded away. Iron staining occurs when the rock is exposed to oxygen and water over long periods.

Field identification & locations

Identify by its hardness (cannot be scratched by a steel knife) and its smooth, waxy texture compared to typical sandstone. Common in river beds and coastal areas.