sedimentary

Banded chert pebble

Microcrystalline quartz (SiO₂), commonly called chert or flint

AI-generated identification · may be incorrect

Hardness about 7 Mohs; dark gray to black with thin curved brown-gray bands, waxy to dull luster, cryptocrystalline structure, and no visible cleavage. It appears water-worn and naturally polished, likely with a specific gravity near 2.6.

Identified September 11, 2026More sedimentary →

Explore Banded chert pebble in the encyclopedia →

Identify your own rocks.

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

App Store Google Play

Physical properties

Formation & geological history

Formed when silica-rich groundwater or marine silica precipitated and replaced sediment, producing microcrystalline quartz; banding records changing impurities or depositional conditions. Chert occurs from Precambrian through modern geological settings, with the specimen likely a beach-transported pebble.

Uses & applications

Used historically for sharp tools and fire-starting, and today as a lapidary or decorative material; attractive banded pieces may be cut or polished for cabochons.

Geological facts

Its extremely fine quartz texture gives it a smooth, conchoidal fracture rather than cleavage. The parallel bands may resemble agate, but the dark opaque appearance is more consistent with banded chert.

Field identification & locations

Identify by its very hard, glass-scratching surface, waxy feel, opaque bands, and conchoidal fracture; it is commonly found in gravel beds, river channels, and pebble beaches. Avoid confusing it with softer shale or slag.