sedimentary

Chert (Jasper variety)

Microcrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 6.5-7 on Mohs scale; Color: Reddish-brown with tan patches; Luster: Dull to waxy; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture)

Hardness: 6
Color: Reddish-brown with tan patches
Luster: Dull to waxy

Identified July 1, 2026More sedimentary →

Explore Chert (Jasper variety) in the encyclopedia →

Identify your own rocks.

Get a report just like this from any photo, free.

App Store Google Play

Physical properties

Hardness: 6.5-7 on Mohs scale; Color: Reddish-brown with tan patches; Luster: Dull to waxy; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture)

Formation & geological history

Formed from the accumulation of silica-rich microfossils like radiolarians or diatoms on the ocean floor, followed by compaction and diagenesis. Common in sedimentary basins worldwide.

Uses & applications

Historically used for making stone tools due to sharp fracture edges; currently used for landscaping, tumbled stones, and semi-precious jewelry.

Geological facts

Chert is so durable it often remains in riverbeds long after surrounding rocks have eroded away. Red varieties colored by iron oxides are specifically called jasper.

Field identification & locations

Identify by its extreme hardness (cannot be scratched by a steel knife) and its smooth, shell-like (conchoidal) fracture surfaces. Commonly found in gravel pits and stream beds.