sedimentary

Chert (Jasper variety)

Silicon Dioxide (SiO2)

Hardness: 6.5-7 Mohs; Color: Reddish-brown, tan, or grey; Luster: Dull to waxy; Structure: Microcrystalline/Cryptocrystalline quartz; Cleavage: None (Conchoidal fracture); Specific Gravity: 2.6

Hardness: 6
Color: Reddish-brown, tan, or grey
Luster: Dull to waxy

Identified June 14, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7 Mohs; Color: Reddish-brown, tan, or grey; Luster: Dull to waxy; Structure: Microcrystalline/Cryptocrystalline quartz; Cleavage: None (Conchoidal fracture); Specific Gravity: 2.6

Formation & geological history

Formed from the precipitation of silica-rich fluids in sedimentary basins or through the replacement of limestone. This specimen appears as a river-worn pebble or aggregate component.

Uses & applications

Used historically for stone tools due to sharp edges; currently used for decorative gravel, landscaping, and occasionally lapidary work/jewelry.

Geological facts

Chert is so hard it can scratch steel and was used for centuries to start fires by striking it against iron or steel. This specific specimen shows rounding from water erosion.

Field identification & locations

Look for a smooth, waxy texture and shell-like (conchoidal) fractures. It is commonly found in gravel pits, riverbeds, and as nodules in limestone outcrops.