mineral

Tumbled agate (likely Botswana or fortification agate)

Microcrystalline quartz, SiO₂ (chalcedony with banded impurities)

AI-generated identification · may be incorrect

Hardness 6.5–7 Mohs; translucent cream, gray, lavender, and brown banding; waxy to vitreous luster; cryptocrystalline quartz with no visible cleavage and conchoidal fracture. The rounded shape indicates tumbling and polishing.

Identified August 9, 2026More mineral →

Explore Tumbled agate (likely Botswana or fortification agate) in the encyclopedia →

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Physical properties

Formation & geological history

Forms when silica-rich groundwater fills cavities in volcanic rock, depositing concentric or irregular chalcedony bands over long periods, commonly during the Cenozoic or older volcanic episodes.

Uses & applications

Used for cabochons, beads, carvings, paperweights, and decorative objects; attractive polished pieces generally have modest collector value.

Geological facts

Agate banding records changing chemistry, temperature, and groundwater conditions during cavity filling. Color may be natural or enhanced by dyeing or heat treatment.

Field identification & locations

Identify by curved, often translucent bands, waxy surface, and quartz-like hardness; it should scratch ordinary glass but not be scratched by steel. Common sources include Brazil, Uruguay, Botswana, India, Madagascar, and Mexico.