mineral

Polished blue agate/geode slice

Chalcedony (microcrystalline quartz, SiO₂), likely dyed blue

AI-generated identification · may be incorrect

Hardness about 6.5–7 Mohs; blue, white, and gray banding with waxy to glassy luster and translucent chalcedony. Quartz has trigonal crystal structure but appears fibrous and lacks visible cleavage; specific gravity is about 2.6.

Identified August 10, 2026More mineral →

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Physical properties

Formation & geological history

Agate forms when silica-rich groundwater fills cavities in volcanic rocks, depositing concentric chalcedony layers over long periods, commonly during the Mesozoic or younger. The vivid blue color is often enhanced by dyeing, and the slab has been cut and polished.

Uses & applications

Used for bookends, decor, cabochons, carvings, and jewelry; attractive polished slices are popular collectors’ specimens.

Geological facts

The dark blue areas may be natural quartz/chalcedony or concentrated dye in porous bands. Agate’s banding records repeated changes in fluid chemistry during cavity filling.

Field identification & locations

Identify by curved bands, translucency, very high hardness, and inability to scratch with a steel knife; dyed material may show color concentrated in cracks or pores. Common sources include Brazil, Uruguay, Mexico, and Madagascar.