mineral

Tumbled agate/chalcedony pebble

Microcrystalline quartz (SiO₂), likely agate or jasper-chalcedony

AI-generated identification · may be incorrect

Hardness about 6.5–7 Mohs; cream-white with dark brown to black curved banding or inclusions, and a smooth waxy to glassy luster. Agate is cryptocrystalline quartz with no visible cleavage and conchoidal fracture; the dark markings may be manganese or iron oxides.

Identified September 7, 2026More mineral →

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Physical properties

Formation & geological history

Forms when silica-rich groundwater fills cavities in volcanic rock, depositing chalcedony and quartz in successive layers; most specimens formed during ancient volcanic episodes, commonly Paleozoic–Cenozoic. The rounded shape and polish indicate natural abrasion or tumbling.

Uses & applications

Used for cabochons, beads, carvings, lapidary pieces, and small decorative specimens; ordinary examples have modest commercial value.

Geological facts

Agate’s banding develops from changing fluid chemistry, temperature, and deposition conditions. A definitive identification requires close examination, translucency, and sometimes testing.

Field identification & locations

Common in volcanic terrains and alluvial gravels worldwide, including Brazil, Uruguay, Mexico, India, Madagascar, and the United States. Look for translucency at thin edges, waxy luster, curved banding, and resistance to scratching by steel.