sedimentary

Chert (Jasper variety)

Silicon Dioxide (SiO2)

Hardness: 6.5-7 Mohs; Color: Brown, tan, and yellowish-cream; Luster: Dull to waxy; Structure: Microcrystalline/Cryptocrystalline; Fracture: Conchoidal; Specific Gravity: 2.6-2.7

Hardness: 6
Color: Brown, tan, and yellowish-cream
Luster: Dull to waxy

Identified July 5, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7 Mohs; Color: Brown, tan, and yellowish-cream; Luster: Dull to waxy; Structure: Microcrystalline/Cryptocrystalline; Fracture: Conchoidal; Specific Gravity: 2.6-2.7

Formation & geological history

Formed through the accumulation of silica-rich marine organisms (like radiolaria or diatoms) or by chemical precipitation in groundwater replacing limestone. This specimen shows a weathered exterior (cortex) and a dark, interior fracture.

Uses & applications

Historically used for stone tools and weapons due to its sharp conchoidal fracture. Today used in jewelry as cabochons, for landscaping, and as a collectible geological specimen.

Geological facts

Chert is so durable that it often survives as stream pebbles long after the surrounding rock has eroded. Dark varieties are often called flint, while colorful or opaque varieties are referred to as jasper.

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 sedimentary basins worldwide.