gemstone

Tumbled agate (likely banded/chalcedony agate)

Microcrystalline quartz, SiO₂; chalcedony with possible iron-oxide coloration

AI-generated identification · may be incorrect

Hardness 6.5–7 Mohs; translucent gray, brown, reddish, and bluish tones; waxy to vitreous luster; cryptocrystalline quartz with no visible cleavage and conchoidal fracture. The rounded shape and smooth polish indicate human tumbling.

Identified September 13, 2026More gemstone →

Explore Tumbled agate (likely banded/chalcedony agate) in the encyclopedia →

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Physical properties

Formation & geological history

Forms when silica-rich groundwater fills cavities in volcanic rocks, depositing chalcedony and quartz in layers; coloration commonly comes from iron and other trace minerals. Individual agate layers may form over thousands to millions of years, often in Paleozoic–Cenozoic volcanic terrains.

Uses & applications

Used for cabochons, beads, paperweights, carvings, and lapidary collectibles; durable but not typically a high-value gemstone.

Geological facts

Agate is a variety of chalcedony, and its banding reflects changing chemistry during cavity filling. Some specimens show fortification, moss, plume, or eye patterns.

Field identification & locations

Identify by testing for hardness near quartz, translucent edges, waxy luster, and curved or banded internal patterns; common sources include Brazil, Uruguay, Mexico, India, Madagascar, and the United States.