mineral

Tumbled banded agate

Microcrystalline quartz (SiO₂), chiefly chalcedony

AI-generated identification · may be incorrect

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

Identified August 28, 2026More mineral →

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Physical properties

Formation & geological history

Agate forms when silica-rich groundwater fills cavities in volcanic rock, depositing chalcedony and quartz in successive layers. Individual bands may develop over thousands to millions of years, commonly in Paleozoic–Cenozoic volcanic terrains.

Uses & applications

Used for lapidary cabochons, carvings, beads, ornamental objects, and inexpensive jewelry; polished slices are also decorative.

Geological facts

The concentric or flowing bands reflect changing chemistry, temperature, and silica saturation during cavity filling. The pale central area may be quartz, chalcedony, or a partly open vug.

Field identification & locations

Identify it by translucent edges, fine parallel or curved banding, waxy luster, and hardness sufficient to scratch glass; it is commonly found in Brazil, Uruguay, Mexico, India, Madagascar, and the western United States.