sedimentary

Banded Chert

Microcrystalline Quartz (SiO2)

Hardness: 7 Mohs scale; Color: Dark grey to black with brown and tan bands; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Hardness: 7 Mohs scale
Color: Dark grey to black with brown and tan bands
Luster: Waxy to dull

Identified July 17, 2026More sedimentary →

Explore Banded 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: 7 Mohs scale; Color: Dark grey to black with brown and tan bands; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Formation & geological history

Formed in marine environments through the accumulation of silica-rich organic remains or chemical precipitation. These bands represent variations in mineral content during deposition over millions of years.

Uses & applications

Historically used for making sharp tools (arrowheads). Currently used for landscaping, as river stones, and for tumbling/polishing by collectors.

Geological facts

Chert is so hard it can strike sparks against steel. This specific specimen’s rounded shape indicates it was water-worn by a river or beach action.

Field identification & locations

Identified by its extreme hardness (cannot be scratched by a steel knife) and smooth, rounded water-worn texture. Commonly found in riverbeds and glacial deposits.