sedimentary

Chert (Jasper variety)

Silicon Dioxide (SiO2)

AI-generated identification · may be incorrect

Hardness: 6.5-7 (Mohs). Color: Brownish-yellow to tan with opaque luster. Crystal structure: Cryptocrystalline (microscopic quartz). Cleavage: None, exhibits conchoidal fracture. Specific gravity: 2.6-2.7.

Hardness: 6
Color: Brownish-yellow to tan with opaque luster

Identified February 19, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the precipitation of silica-rich fluids within sedimentary rock layers like limestone or through the accumulation of siliceous organisms. Often Mesozoic to Cenozoic in age depending on the local basin.

Uses & applications

Used historically for stone tools due to sharp edges when fractured. Modern uses include decorative landscaping, tumbling for jewelry/beads, and as an industrial abrasive.

Geological facts

Chert is so durable that it often survives as smooth river pebbles long after the surrounding host rock has eroded away. Certain colorful varieties are highly sought after by lapidaries.

Field identification & locations

Identify by its extreme hardness (will scratch glass/steel) and smooth, waxy feel when wet. Commonly found in riverbeds, gravel pits, and coastal regions as rounded cobbles.