sedimentary

Banded chert pebble

Microcrystalline quartz (SiO₂), likely ferruginous or jaspery chert

AI-generated identification · may be incorrect

Hardness about 6.5–7 Mohs; brown-tan, fine-grained, and waxy to dull luster with pale streaks and a dark weathering rind. It has no visible crystals or cleavage and commonly breaks with conchoidal fracture; the rounded shape indicates water abrasion.

Identified September 4, 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

Chert forms when silica-rich sediment or biogenic silica recrystallizes into microcrystalline quartz, commonly in marine limestone or volcanic-sediment settings. The pebble was later transported and rounded in a river, beach, or glacial deposit; its exact age cannot be determined from the image.

Uses & applications

Used historically for sharp tools and occasionally as a decorative stone, landscaping pebble, or lapidary material. Attractive patterned pieces may be polished, though this specimen appears naturally water-worn.

Geological facts

The dark outer band may be a weathering cortex or iron/manganese-rich zone rather than a true layer. Chert can produce exceptionally sharp edges when fractured.

Field identification & locations

Identify by its very fine texture, hardness, lack of visible grains, and glassy/conchoidal fracture; it should resist scratching by a steel blade. Common in sedimentary terrains, river gravels, beaches, and glacial tills.