gemstone

Tumbled agate or chalcedony

Microcrystalline quartz (SiO₂), likely agate/chalcedony

AI-generated identification · may be incorrect

Polished, rounded pebble with translucent brown-gold and gray zones, waxy to vitreous luster, and probable cryptocrystalline quartz structure; Mohs hardness 6.5–7, no cleavage, specific gravity about 2.6. The visible circular texture may be an agate band or an inclusion rather than a crystal.

Identified September 18, 2026More gemstone →

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Physical properties

Formation & geological history

Forms when silica-rich groundwater fills cavities in volcanic rock, commonly during the Cenozoic or older volcanic episodes; later weathering releases it as a pebble and tumbling produces the smooth shape.

Uses & applications

Used for cabochons, beads, carvings, paperweights, and ornamental objects; this small tumbled specimen has modest commercial value.

Geological facts

Agate’s fine bands and translucency result from repeated silica deposition, while chalcedony is its generally unbanded microcrystalline form.

Field identification & locations

Identify by its glassy/waxy luster, translucency, hardness, and inability to scratch it with a steel knife; common sources include Brazil, Uruguay, India, Mexico, Madagascar, and the western United States.