sedimentary

Chert (Jasper/Mudstone variety with Oxidation)

Silicon dioxide (SiO2)

AI-generated identification · may be incorrect

Hardness: 6.5-7 (Mohs), Color: Tan, brown, and yellow-orange (due to iron oxides), Luster: Dull to waxy, Crystal Structure: Microcrystalline (Cryptocrystalline), Cleavage: None (conchoidal fracture).

Hardness: 6

Identified June 8, 2026More sedimentary →

Explore Chert (Jasper/Mudstone variety with Oxidation) 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 (Mohs), Color: Tan, brown, and yellow-orange (due to iron oxides), Luster: Dull to waxy, Crystal Structure: Microcrystalline (Cryptocrystalline), Cleavage: None (conchoidal fracture).

Formation & geological history

Formed through the accumulation of silica-rich organic remains or chemical precipitation in sedimentary environments. The distinct layering and 'rind' are results of chemical weathering and oxidation (limonite staining) over geologic time.

Uses & applications

Historically used for stone tools/arrowheads. Today used for landscaping, as a minor gemstone (jasper), and for fire-starting (flint).

Geological facts

The yellow-orange outer layer is often called a 'weathering rind,' caused by the oxidation of iron-bearing minerals within the rock once exposed to oxygen and water.

Field identification & locations

Look for a smooth, waxy surface on broken edges and a sharp, shell-like (conchoidal) fracture pattern. Commonly found in riverbeds and limestone deposits.