mineral

Tumbled agate

Microcrystalline quartz (SiO₂), chiefly chalcedony with possible translucent quartz bands

AI-generated identification · may be incorrect

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

Identified August 25, 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 specimens commonly formed during volcanic episodes from the Paleozoic to Cenozoic, depending on locality.

Uses & applications

Used for cabochons, beads, carvings, bookends, and decorative polished stones; durable agate is also used for burnishing tools and ornamental objects.

Geological facts

Its bands reflect changing chemistry, temperature, and fluid conditions during cavity filling. The specimen may also be jaspery chalcedony rather than a sharply banded agate.

Field identification & locations

Identify by hardness, translucency, curved/concentric banding, and resistance to scratching by steel; it should scratch glass but not be scratched by a knife. Common sources include Brazil, Uruguay, Mexico, India, Madagascar, and the western United States.