mineral

Polished banded agate (likely carnelian agate)

Microcrystalline quartz, SiO₂ (chalcedony); iron oxides produce the orange-red bands

AI-generated identification · may be incorrect

Hardness 6.5–7 Mohs; translucent orange, red, white, and gray banding; vitreous to waxy luster; cryptocrystalline quartz with no visible cleavage and conchoidal fracture. The image also includes assorted tumbled stones, but the prominent slab is agate.

Identified September 4, 2026More mineral →

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Physical properties

Formation & geological history

Forms when silica-rich groundwater fills cavities in volcanic rock, depositing chalcedony in successive layers; typically Phanerozoic, though agate occurs in rocks of many ages. Common sources include Brazil, Uruguay, India, Madagascar, Mexico, and the United States.

Uses & applications

Used for cabochons, jewelry, carvings, bookends, display slabs, and lapidary items; durable ornamental stone rather than a major construction material.

Geological facts

Its curved, parallel bands reflect changing chemistry during repeated silica deposition. Red-orange coloration generally comes from microscopic hematite or limonite inclusions.

Field identification & locations

Identify by translucent concentric or irregular bands, waxy appearance, and quartz hardness: it scratches glass but not vice versa. Common in volcanic geodes and alluvial gravel; avoid confusing dyed chalcedony with naturally vivid material.