sedimentary

Chert

Chert (SiO2, Silicon Dioxide)

AI-generated identification · may be incorrect

Hardness: 6.5-7 Mohs. Color: Gray, tan, or brown. Luster: Waxy to dull. Structure: Microcrystalline/cryptocrystalline quartz. Cleavage: None (conchoidal fracture).

Hardness: 6
Color: Gray, tan, or brown
Luster: Waxy to dull

Identified July 4, 2026More sedimentary →

Explore Chert 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: Gray, tan, or brown. Luster: Waxy to dull. Structure: Microcrystalline/cryptocrystalline quartz. Cleavage: None (conchoidal fracture).

Formation & geological history

Formed in marine environments through the accumulation of siliceous organisms or chemical precipitation. Many specimens date from the Paleozoic or Mesozoic eras.

Uses & applications

Historically used for stone tools (arrowheads). Modern uses include road surfacing and as a raw material for silicon-based products. Often collected as river stones.

Geological facts

Chert is so hard it can create sparks when struck against steel. It is chemically similar to flint, but 'flint' usually refers specifically to dark nodules found in chalk.

Field identification & locations

Identify by its extreme hardness (scratches glass), waxy texture when wet, and curved, shell-like (conchoidal) fractures. Found worldwide in riverbeds and limestone outcrops.