sedimentary

Chert (Jasper)

Silicon dioxide (SiO2)

Hardness: 6.5-7.0 (Mohs). Color: Brownish-red to tan. Luster: Dull to waxy. Structure: Cryptocrystalline. Cleavage: None (conchoidal fracture). Specific gravity: 2.6-2.7.

Hardness: 6
Color: Brownish-red to tan
Luster: Dull to waxy

Identified July 20, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7.0 (Mohs). Color: Brownish-red to tan. Luster: Dull to waxy. Structure: Cryptocrystalline. Cleavage: None (conchoidal fracture). Specific gravity: 2.6-2.7.

Formation & geological history

Formed through the accumulation of silica-rich microfossils (like radiolaria or diatoms) or by chemical precipitation in saltwater or groundwater. Often occurs as nodules in limestone or chalk.

Uses & applications

Historically used for stone tools (knapping) due to its sharp edges. Currently used as an industrial abrasive, in construction aggregate, and as a decorative stone or lapidary material.

Geological facts

Chert was one of the first materials harvested by early humans to make arrowheads and scrapers. Because of its high silica content, it produces sparks when struck against steel.

Field identification & locations

Identify by its extreme hardness (cannot be scratched by a steel knife) and its smooth, shell-like (conchoidal) fracture surfaces. Common in riverbeds and limestone outcrops worldwide.