sedimentary

Chert (Jasper variety)

Silicon Dioxide (SiO2)

Hardness: 6.5-7 (Mohs), Color: Reddish-brown to tan, Luster: Dull to waxy, Crystal Structure: Microcrystalline/Cryptocrystalline, Fracture: Conchoidal

Hardness: 6

Identified July 4, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7 (Mohs), Color: Reddish-brown to tan, Luster: Dull to waxy, Crystal Structure: Microcrystalline/Cryptocrystalline, Fracture: Conchoidal

Formation & geological history

Formed from the recrystallization of silica-rich fluids within sedimentary rock layers, often associated with ancient seafloors and hydrothermal activity.

Uses & applications

Historically used for making stone tools; currently used in jewelry (as a gemstone), landscaping, and as a decorative specimen for collectors.

Geological facts

Chert is so durable that it can survive long periods of weathering and transport by water, which is why it is frequently found as rounded pebbles in gravel pits and stream beds.

Field identification & locations

Identify in the field by its hardness (it can scratch glass), its smooth conchoidal fracture, and its lack of visible grains. Common in limestone regions and river beds.