sedimentary

Chert (Yellow Jasper/Flint)

Silicon Dioxide (SiO2)

Hardness: 7 on Mohs scale; Color: Tan, yellow, or light brown due to iron oxide impurities; Luster: Dull to waxy; Crystal Structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6

Hardness: 7 on Mohs scale
Color: Tan, yellow, or light brown due to iron oxide impurities
Luster: Dull to waxy

Identified March 14, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or the chemical replacement of limestone/dolomite by silica-rich fluids. This specimen appears to be a river-worn or weathered nodule.

Uses & applications

Historically used for stone tools and weapons due to sharp fractures; currently used for decorative landscaping, road aggregate, and as a semi-precious gemstone (Jasper) in jewelry.

Geological facts

Chert is so durable that it often survives long after the surrounding rock has eroded away. Because of its hardness, it was one of the most important minerals for early humans to create fire and hunting tools.

Field identification & locations

Identify in the field by its extreme hardness (cannot be scratched by a steel knife) and its smooth, shell-like (conchoidal) fracture surfaces. Commonly found in riverbeds, glacial till, and limestone outcrops across North America and Europe.

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