mineral

Tumbled agate/chalcedony (likely moss or plume agate)

Microcrystalline quartz, SiO₂; chalcedony with iron-oxide or mineral inclusions

AI-generated identification · may be incorrect

Hardness 6.5–7 Mohs; brown, gray, cream, and reddish coloration with cloudy or dendritic patterns; waxy to vitreous luster; cryptocrystalline structure and no visible cleavage. The rounded, polished surface indicates tumbling.

Identified August 29, 2026More mineral →

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Physical properties

Formation & geological history

Forms when silica-rich groundwater fills cavities in volcanic rock, depositing chalcedony in layers and trapping iron or other mineral inclusions. Most agates formed during the Cenozoic to Paleozoic eras, depending on locality.

Uses & applications

Used for jewelry, cabochons, carvings, and ornamental objects; common tumbled specimens have modest collector value.

Geological facts

Agate is a variety of chalcedony rather than a separate mineral species. Its internal patterns develop incrementally as changing fluids deposit successive silica layers.

Field identification & locations

Identify by its waxy polish, translucency at thin edges, hardness, and absence of cleavage; common sources include Brazil, Uruguay, Mexico, India, Madagascar, and the western United States. A definitive locality or variety requires close inspection or testing.