mineral

Tumbled banded agate

Chalcedony (microcrystalline quartz), SiO₂

AI-generated identification · may be incorrect

Hardness 6.5–7 Mohs; brown, cream, and gray concentric or wavy bands; waxy to vitreous luster; cryptocrystalline quartz with no visible cleavage and conchoidal fracture. The smooth shape indicates mechanical tumbling and polishing.

Identified September 17, 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. Exact variety and locality cannot be confirmed from the photograph.

Uses & applications

Used for cabochons, beads, ornaments, paperweights, and inexpensive collector specimens; durable enough for some decorative stonework.

Geological facts

Banded agate is identified by contrasting chalcedony layers, often enhanced by natural iron or manganese staining. Common sources include Brazil, Uruguay, India, Madagascar, Mexico, and the United States.

Field identification & locations

Field identification: glassy/waxy luster, translucent edges, curved banding, hardness sufficient to scratch ordinary glass, and absence of cleavage. A streak test is white; acid causes no reaction.