mineral

Tumbled banded agate

Microcrystalline quartz (chalcedony), SiO₂, with layered impurities

AI-generated identification · may be incorrect

Hardness 6.5–7 Mohs; gray, blue-gray, cream, and brown rhythmic bands; waxy to glassy luster; cryptocrystalline quartz with no visible cleavage and conchoidal fracture. The smooth rounded shape indicates tumbling and polishing.

Identified August 29, 2026More mineral →

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Physical properties

Formation & geological history

Agate forms when silica-rich groundwater fills cavities in volcanic rock, depositing chalcedony in successive layers. Individual bands may record changing chemistry over thousands to millions of years; common sources include Brazil, Uruguay, Mexico, India, and the United States.

Uses & applications

Used for cabochons, beads, carvings, ornaments, and inexpensive collectible stones; polished agate is also used decoratively and occasionally for small architectural objects.

Geological facts

The banding reflects alternating chalcedony, quartz, and iron- or manganese-bearing layers. Its exact variety cannot be determined confidently from the photograph alone.

Field identification & locations

Identify by concentric or wavy bands, translucent edges, waxy polish, and quartz-like hardness; it should resist scratching by a steel blade. Common rough material occurs in volcanic geodes and stream gravels.