mineral

Tumbled gray agate/chalcedony (probable)

Microcrystalline quartz, SiO₂; likely banded chalcedony or agate

AI-generated identification · may be incorrect

Hardness 6.5–7 Mohs; pale gray to white with darker gray-brown bands or inclusions, waxy to dull luster, cryptocrystalline structure, and no visible cleavage. The rounded shape indicates tumbling or natural water wear.

Identified August 17, 2026More mineral →

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Physical properties

Formation & geological history

Forms when silica-rich groundwater fills cavities in volcanic rocks, depositing layered chalcedony over long periods, commonly during the Cenozoic or older volcanic episodes. Exact identification and age require locality information and testing.

Uses & applications

Used for lapidary items, cabochons, beads, carvings, and ornamental stone; common pieces have modest collector value.

Geological facts

Agate is defined by internal banding or patterned chalcedony, while unbanded material is generally called chalcedony. Brown spots may represent iron oxides or mineral inclusions.

Field identification & locations

Look for translucency at thin edges, waxy luster, curved banding, and quartz-like hardness; it should scratch glass but not be scratched by a steel knife. Common worldwide, especially in volcanic regions of Brazil, Uruguay, Mexico, India, and the United States.