mineral

Polished/sectioned agate geode

Microcrystalline quartz (SiO₂), chiefly chalcedony with possible druzy quartz

AI-generated identification · may be incorrect

Typically hardness 6.5–7 Mohs, waxy to vitreous luster, curved banding, and white/cream chalcedony surrounding a hollow cavity lined with tiny quartz crystals. This specimen appears cut or naturally broken and polished, with minor iron-oxide staining.

Identified August 17, 2026More mineral →

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Physical properties

Formation & geological history

Forms when silica-rich groundwater fills cavities in volcanic rock; successive layers of chalcedony grow inward, often leaving a central vug for later quartz crystallization. Most agates formed in Phanerozoic volcanic environments, commonly hundreds of millions of years old.

Uses & applications

Used as lapidary material, cabochons, ornaments, bookends, and collector specimens; small geodes have modest decorative value.

Geological facts

Agate’s concentric bands record repeated changes in fluid chemistry and silica deposition. The cavity is a geode-like vug rather than a fossil opening.

Field identification & locations

Identify by its very fine, curved chalcedony banding, translucent edges, quartz sparkle, and inability to scratch it with a steel knife easily; common sources include Brazil, Uruguay, Mexico, India, and the western United States.