mineral

Polished blue banded agate slice

Agate, a microcrystalline variety of quartz (SiO₂), commonly with chalcedony

AI-generated identification · may be incorrect

Hardness 6.5–7 Mohs; blue-gray concentric banding, vitreous to waxy luster, cryptocrystalline structure, no visible cleavage, and specific gravity about 2.6. The bright blue color may be natural but is often enhanced by dyeing.

Identified September 7, 2026More mineral →

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Physical properties

Formation & geological history

Agate forms when silica-rich groundwater fills cavities in volcanic rocks, depositing chalcedony and quartz in successive bands. Most specimens are Cenozoic to older volcanic-hosted material; this slice is polished and likely cut from a geode or amygdule.

Uses & applications

Used for cabochons, ornaments, bookends, tabletops, and lapidary collections; banded slices are popular decorative specimens.

Geological facts

Concentric bands record changing chemistry, temperature, and fluid conditions during cavity filling. The central triangular opening appears to be a vug or irregular cavity lined with pale quartz/chalcedony.

Field identification & locations

Identify it by curved concentric bands, translucent edges, waxy chalcedony texture, and hardness sufficient to scratch ordinary glass. Common sources include Brazil, Uruguay, Mexico, India, Madagascar, and the United States.