sedimentary

Banded Chert

Silicon Dioxide (SiO2)

Hardness: 6.5-7 (Mohs scale); Color: Gray, tan, and dark black bands; Luster: Waxy to vitreous; Crystal structure: Cryptocrystalline; Cleavage: None (Conchoidal fracture); Specific gravity: 2.6

Hardness: 6
Color: Gray, tan, and dark black bands
Luster: Waxy to vitreous

Identified May 31, 2026More sedimentary →

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 scale); Color: Gray, tan, and dark black bands; Luster: Waxy to vitreous; Crystal structure: Cryptocrystalline; Cleavage: None (Conchoidal fracture); Specific gravity: 2.6

Formation & geological history

Formed through the precipitation of silica-rich fluids or the accumulation of siliceous microfossils like radiolaria on the ocean floor. The banding often represents seasonal or periodic changes in sediment deposition.

Uses & applications

Historically used for stone tools due to its sharp edges; used today as decorative river rock, in landscaping, and occasionally by lapidary hobbyists for tumbling.

Geological facts

Flint is a variety of chert. Banded chert can sometimes resemble agate, but it is opaque rather than translucent. It is one of the most durable sedimentary rocks on Earth.

Field identification & locations

Identify by its extreme hardness (cannot be scratched by a steel knife) and smooth, waxy surface when water-worn. Common in river beds, beaches, and limestone outcrops.