sedimentary

Chert (Jasper variety)

Silicon Dioxide (SiO2)

Hardness: 6.5-7 on Mohs scale; Color: Tan, brown, reddish-brown with white quartz veining; Luster: Waxy to vitreous; Crystal Structure: Cryptocrystalline (microscopic quartz crystals); Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Hardness: 6
Color: Tan, brown, reddish-brown with white quartz veining
Luster: Waxy to vitreous

Identified June 17, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of silica-rich fluids in sedimentary environments or by the replacement of carbonate rocks. Often found in nodules or bedded deposits within limestone or dolomite.

Uses & applications

Historically used for making stone tools (arrowheads/scrapers) due to its sharp edges; and currently used in jewelry (lapidary), as aquarium stone, and as a decorative rock for collectors.

Geological facts

Chert is so durable that it survives long after surrounding rocks have eroded away. It was one of the first materials used by early humans to create fire by striking it against iron pyrite.

Field identification & locations

Identified in the field by its hardness (cannot be scratched by a steel knife), concave (conchoidal) fractures that resemble glass, and a waxy texture. Commonly found in stream beds and coastal gravels.