sedimentary

Chert with Iron Oxide Staining

Microcrystalline Quartz (SiO2) with Limonite/Goethite staining

AI-generated identification · may be incorrect

Hardness: 7 (Mohs scale), Color: White/Grey interior with rusty orange/brown surface, Luster: Waxy to dull, Crystal structure: Cryptocrystalline, Cleavage: None (conchoidal fracture)

Identified June 1, 2026More sedimentary →

Explore Chert with Iron Oxide Staining in the encyclopedia →

Identify your own rocks.

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

App Store Google Play

Physical properties

Hardness: 7 (Mohs scale), Color: White/Grey interior with rusty orange/brown surface, Luster: Waxy to dull, Crystal structure: Cryptocrystalline, Cleavage: None (conchoidal fracture)

Formation & geological history

Formed from the accumulation of silica-rich organic remains or chemical precipitation in marine or groundwater environments. The orange staining is a secondary process involving the weathering of iron-rich minerals.

Uses & applications

Historically used for making stone tools (flint knapping) due to its sharp edges; used today as a decorative rock or road aggregate.

Geological facts

Chert was one of the most important minerals for early humans, used for spearheads and fire-starting. The orange crust is essentially a form of biological or chemical rust.

Field identification & locations

Identified in the field by its extreme hardness (cannot be scratched by a steel knife) and its smooth, shell-like (conchoidal) fracture pattern. Commonly found in limestone beds.