mineral

Polished banded agate

Chalcedony (microcrystalline quartz), SiO₂

AI-generated identification · may be incorrect

Hardness 6.5–7 Mohs; cream, tan, and brown concentric/flowing bands; waxy to glassy luster; cryptocrystalline quartz with no visible cleavage and conchoidal fracture. The rounded shape indicates tumbling or polishing.

Identified September 20, 2026More mineral →

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Physical properties

Formation & geological history

Forms when silica-rich groundwater fills cavities in volcanic rocks, depositing successive layers of chalcedony over long periods, commonly during the Cenozoic or older. Typical sources include Brazil, Uruguay, Mexico, India, Madagascar, and the western United States.

Uses & applications

Used for cabochons, beads, carvings, ornaments, and lapidary collections; durable polished pieces are inexpensive jewelry materials.

Geological facts

Agate banding records changing chemistry, temperature, and fluid conditions during cavity filling. Its patterns and translucency vary greatly even within one specimen.

Field identification & locations

Identify by hardness, waxy luster, fine banding, and inability to scratch with a steel knife easily; glassy imitations may show bubbles or uniform color. Exact species and locality require magnification or testing.