gemstone

Tumbled agate

Microcrystalline quartz (chalcedony), SiO₂

AI-generated identification · may be incorrect

Hardness about 6.5–7 Mohs; translucent brown, cream, gray, and reddish material with waxy to vitreous luster. The specimen shows mottled/banded chalcedony and likely iron-oxide inclusions; no visible cleavage, conchoidal fracture.

Identified September 6, 2026More gemstone →

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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. Its age depends on the host lava, commonly Paleozoic to Cenozoic; this piece has been cut or naturally weathered and polished/tumbled.

Uses & applications

Used for cabochons, beads, carvings, bookends, and decorative objects; durable tumbled pieces are popular inexpensive collectibles.

Geological facts

Agate is a variety of chalcedony, and its patterns arise from changing silica chemistry, impurities, and growth conditions. Brown coloration commonly reflects iron oxides or hydroxides.

Field identification & locations

Identify it by its waxy translucence, conchoidal edges, and curved or mottled chalcedony pattern; common sources include Brazil, Uruguay, Mexico, India, Madagascar, and the United States. A scratch test should not mark it with a steel knife, though testing can damage the specimen.