mineral

Tumbled agate/chalcedony pebble

Microcrystalline quartz (SiO₂), likely agate or jasper variety

AI-generated identification · may be incorrect

Hardness 6.5–7 Mohs; cream to honey-brown with translucent, waxy-to-glassy luster and faint concentric/botryoidal banding. It is cryptocrystalline, with no visible cleavage and conchoidal fracture; the rounded shape indicates natural abrasion or tumbling.

Identified August 29, 2026More mineral →

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Physical properties

Formation & geological history

Formed when silica-rich groundwater filled cavities in volcanic rock, depositing chalcedony and quartz in successive layers. The exact geological age cannot be determined from the photograph; agates occur in rocks from many ages worldwide.

Uses & applications

Used for cabochons, beads, carvings, tumbled stones, and inexpensive jewelry; larger agate is also used for ornaments and polished slabs.

Geological facts

The brown center may be iron-oxide staining or a small druzy/quartz-filled cavity. Agate is defined by patterned chalcedony banding, while less-banded material may be called jasper or chalcedony.

Field identification & locations

Common in volcanic terrains, river gravels, and beaches, especially Brazil, Uruguay, Mexico, the western United States, India, and Madagascar. Check for translucency, waxy luster, hardness, and curved/concentric banding; glass imitators usually show bubbles or uniform color.