sedimentary

Chert (Jasper)

Silicon Dioxide (SiO2)

Hardness: 6.5-7 on Mohs scale; Color: Reddish-brown, tan, and cream mottled; Luster: Waxy to dull; Crystal structure: Microcrystalline/Cryptocrystalline; Cleavage: None (Conchoidal fracture)

Hardness: 6
Color: Reddish-brown, tan, and cream mottled
Luster: Waxy to dull

Identified June 30, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7 on Mohs scale; Color: Reddish-brown, tan, and cream mottled; Luster: Waxy to dull; Crystal structure: Microcrystalline/Cryptocrystalline; Cleavage: None (Conchoidal fracture)

Formation & geological history

Formed from the accumulation of silica-rich microfossils (like radiolaria or diatoms) or through chemical precipitation in marine or groundwater environments.

Uses & applications

Historically used for stone tools/arrowheads; currently used for lapidary work, jewelry, and landscaping. High-quality specimens are popular for rock tumbling.

Geological facts

Chert has been used by humans for millions of years because it breaks with a razor-sharp edge. When it is red or multi-colored, it is often specifically called Jasper.

Field identification & locations

Identify by its hardness (cannot be scratched by a steel knife) and its smooth, shell-like (conchoidal) fracture surface. Common in riverbeds and sedimentary basins worldwide.