mineral

Tumbled banded agate

Microcrystalline quartz (chalcedony), SiO₂, with band-forming impurities

AI-generated identification · may be incorrect

Hardness 6.5–7 Mohs; blue-gray, cream, and dark concentric bands; waxy to dull luster; cryptocrystalline quartz with no visible cleavage and conchoidal fracture. Specific gravity is about 2.6.

Identified September 12, 2026More mineral →

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Physical properties

Hardness 6.5–7 Mohs; blue-gray, cream, and dark concentric bands; waxy to dull luster; cryptocrystalline quartz with no visible cleavage and conchoidal fracture. Specific gravity is about 2.6.

Formation & geological history

Forms when silica-rich groundwater fills cavities in volcanic rock, depositing successive layers of chalcedony, often over millions of years. The specimen appears cut or naturally rounded and polished/tumbled.

Uses & applications

Used for cabochons, beads, ornaments, paperweights, and lapidary displays; durable and popular in inexpensive jewelry.

Geological facts

Agate banding records changing chemistry and fluid conditions during cavity filling. Individual patterns are highly variable, making each polished piece distinctive.

Field identification & locations

Identify by its fine concentric or irregular bands, translucency at thin edges, waxy surface, and lack of cleavage; common sources include Brazil, Uruguay, Mexico, India, and the United States. A hardness test should not scratch it with a steel knife.