sedimentary

Chert (Jasper/Flint variant)

Silicon Dioxide (SiO2)

Hardness: 6.5-7 (Mohs shell), Color: Light grayish-green with dark vein inclusions, Luster: Waxy to vitreous, Crystal Structure: Microcrystalline/Cryptocrystalline (Trigonal), Cleavage: None (Conchoidal fracture), Specific Gravity: 2.6-2.7

Hardness: 6

Identified May 7, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed from the recrystallization of silica-rich fluids or the accumulation of siliceous remains (like diatoms or radiolaria) in marine environments. The veins visible are secondary silica or mineral fills within fractures (tension gashes).

Uses & applications

Historically used for stone tools and weapons due to its sharp conchoidal fracture. Industrially used as an abrasive, and aesthetically used for lapidary work, cabochons, and decorative pebbles.

Geological facts

Chert is so durable that it can survive long-distance transport in rivers and glacial activity, which is why it is often found as smooth river cobbles. The visible 'cross' pattern is a result of structural stress creating perpendicular fractures later filled by minerals.

Field identification & locations

Identify by its extreme hardness (cannot be scratched by a steel knife) and its smooth, waxy surface. Look for the distinctive conchoidal (shell-like) fracture patterns on broken edges. Commonly found in river beds and coastal areas.

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