sedimentary

Chert (variations include Flint/Jasper)

Chert (SiO2)

AI-generated identification · may be incorrect

Hardness: 6.5-7. Color: Gray, brown, rusty orange-red. Luster: Waxy to dull. Crystal structure: Cryptocrystalline. Cleavage: None (has conchoidal fracture). Specific Gravity: 2.5-2.8.

Hardness: 6
Color: Gray, brown, rusty orange-red
Luster: Waxy to dull

Identified April 15, 2026More sedimentary →

Explore Chert (variations include Flint/Jasper) 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. Color: Gray, brown, rusty orange-red. Luster: Waxy to dull. Crystal structure: Cryptocrystalline. Cleavage: None (has conchoidal fracture). Specific Gravity: 2.5-2.8.

Formation & geological history

Formed from the accumulation of microscopic silica-rich organisms or chemical precipitation of silica in marine environments. Often found as nodules within limestone or chalk beds.

Uses & applications

Historically used for stone tools (arrowheads). Modern uses include road surfacing, jewelry (when colorful), and industrial abrasives.

Geological facts

Because it breaks with a sharp edge, it was the primary material for prehistoric survival. It is so hard that it can strike sparks from steel, hence its related name 'flint'.

Field identification & locations

Identify by its 'waxy' texture and shell-like (conchoidal) breakage patterns. Look for it in riverbeds or eroding limestone cliffs. It is resistant to weathering and often appears as rounded river cobbles like this one.