sedimentary

Polished banded chert (likely agate-like chalcedony)

Microcrystalline quartz, SiO₂; chalcedony with iron-oxide banding

AI-generated identification · may be incorrect

Hardness about 6.5–7 Mohs; cream, tan, and brown curved bands; waxy to vitreous luster; cryptocrystalline quartz with no visible cleavage and conchoidal fracture. The smooth surface indicates tumbling or polishing.

Identified August 30, 2026More sedimentary →

Explore Polished banded chert (likely agate-like chalcedony) 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 filled cavities or replaced material in volcanic or sedimentary rocks, depositing successive layers of chalcedony; banding may reflect changing iron content. Exact geological age and locality cannot be determined from the image.

Uses & applications

Used as a lapidary ornamental stone, cabochon, paperweight, and collector specimen; durable but generally not a high-value gemstone.

Geological facts

The specimen resembles banded chert or a jasper–chalcedony mixture rather than a confirmed agate; translucent edges and sharper concentric banding would support agate identification.

Field identification & locations

Common in silica-rich gravels and volcanic terrains worldwide, including Brazil, Uruguay, Mexico, the western United States, and Madagascar. Field clues are its very hard surface, waxy appearance, curved bands, and inability to scratch with a steel knife.