sedimentary

Chert (Iron-stained)

Microcrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 Mohs scale; Color: Brown, tan, reddish-orange due to iron oxides; Luster: Dull to waxy; Structure: Cryptocrystalline/Microcrystalline; Cleavage: None (conchoidal fracture).

Hardness: 7 Mohs scale
Color: Brown, tan, reddish-orange due to iron oxides
Luster: Dull to waxy

Identified June 6, 2026More sedimentary →

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Physical properties

Hardness: 7 Mohs scale; Color: Brown, tan, reddish-orange due to iron oxides; Luster: Dull to waxy; Structure: Cryptocrystalline/Microcrystalline; Cleavage: None (conchoidal fracture).

Formation & geological history

Formed primarily as a chemical precipitate from silica-rich fluids in sedimentary environments. Common in marine deposits where silica from radiolarians or sponges accumulates.

Uses & applications

Historically used for stone tools due to conchoidal fracturing. Modernly used as construction aggregate, decorative landscaping stone, and occasionally for lapidary work.

Geological facts

Chert is so durable that it often survives as rounded pebbles in streambeds long after the surrounding rock has weathered away. It is often found as nodules inside limestone.

Field identification & locations

Identify by its extreme hardness (cannot be scratched by a steel knife) and its smooth, shell-like (conchoidal) fracture surfaces. Commonly found in riverbeds and glacial till.