sedimentary

Chert (Iron-stained)

Chert (Microcrystalline and Cryptocrystalline Quartz, SiO2)

AI-generated identification · may be incorrect

Hardness: 7 (Mohs scale), Color: Brown to tan with reddish-orange iron oxide staining, Luster: Waxy to dull, Structure: Cryptocrystalline, Cleavage: None (conchoidal fracture), Specific Gravity: 2.65

Identified March 26, 2026More sedimentary →

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Physical properties

Hardness: 7 (Mohs scale), Color: Brown to tan with reddish-orange iron oxide staining, Luster: Waxy to dull, Structure: Cryptocrystalline, Cleavage: None (conchoidal fracture), Specific Gravity: 2.65

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like radiolarians or diatoms) or by chemical precipitation in ground water. This specimen appears to have undergone significant weathering and oxidation of iron impurities.

Uses & applications

Historically used for stone tools and arrowheads. Currently used as an abrasive, in road construction (aggregate), and occasionally for lapidary work if highly patterned.

Geological facts

Chert is so hard it can produce sparks when struck against steel, which made it vital for prehistoric fire-making. It is one of the most chemically stable and durable rocks in Earth's crust.

Field identification & locations

Identify in the field by its extreme hardness (cannot be scratched by a steel blade) and its sharp, shell-like (conchoidal) fractures. Common in limestone formations. Look for smooth, waxy surfaces on fresh breaks.