mineral

Polished blue-banded agate slice

Agate (microcrystalline quartz, SiO₂; chiefly chalcedony)

AI-generated identification · may be incorrect

Hardness 6.5–7 Mohs; translucent blue-gray, white, and brown concentric banding; waxy to vitreous luster; cryptocrystalline with no visible cleavage and conchoidal fracture. The central cavity may contain druzy quartz or iron-oxide staining.

Identified August 7, 2026More mineral →

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Physical properties

Formation & geological history

Forms when silica-rich groundwater repeatedly fills gas bubbles or cavities in volcanic rocks, depositing chalcedony in successive layers. Individual bands may form over thousands to millions of years, commonly in Cenozoic volcanic provinces.

Uses & applications

Cut slices are used for jewelry, cabochons, bookends, coasters, and decorative objects; uncommon vivid blue banding increases appeal to collectors.

Geological facts

Agate is a variety of chalcedony, and its band patterns are diagnostic growth records. Natural blue tones are possible, though intensely electric blue agates are often dyed.

Field identification & locations

Identify it by concentric curved bands, translucency at the edges, waxy luster, and hardness sufficient to scratch glass. Common sources include Brazil, Uruguay, Mexico, India, and the United States.