mineral

Tumbled agate/chalcedony

Microcrystalline quartz (SiO₂), likely mossy or dendritic agate

AI-generated identification · may be incorrect

Hardness 6.5–7 Mohs; translucent gray-white to brown with a waxy-to-glassy luster and possible iron-oxide or mineral inclusions. Quartz is trigonal, but its microscopic fibrous structure produces no visible cleavage and conchoidal fracture.

Identified August 25, 2026More mineral →

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Physical properties

Formation & geological history

Forms when silica-rich groundwater fills cavities in volcanic rock, depositing layered chalcedony and later inclusions over long geological periods, commonly in Cenozoic to older volcanic formations. The specimen has been cut and/or tumbled and polished.

Uses & applications

Used for cabochons, beads, carvings, ornaments, and inexpensive collector specimens; agate is also used in decorative stonework and industrial precision surfaces.

Geological facts

Agate’s fine bands or plume-like inclusions arise from repeated silica deposition and trapped impurities. Its color may be enhanced by dyeing, though this piece appears relatively natural.

Field identification & locations

Identify by testing its glassy/conchoidal appearance, translucency, lack of cleavage, and hardness— it should scratch ordinary glass but not be scratched by steel easily. Common sources include Brazil, Uruguay, Mexico, India, Madagascar, and the western United States.