mineral

Polished banded agate

Microcrystalline quartz (chalcedony), SiO₂, with iron-oxide and clay inclusions

AI-generated identification · may be incorrect

Hardness 6.5–7; translucent brown, honey, gray, and cream bands; waxy to vitreous luster; cryptocrystalline quartz with no visible cleavage, conchoidal fracture, and specific gravity about 2.6.

Identified September 15, 2026More mineral →

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Physical properties

Hardness 6.5–7; translucent brown, honey, gray, and cream bands; waxy to vitreous luster; cryptocrystalline quartz with no visible cleavage, conchoidal fracture, and specific gravity about 2.6.

Formation & geological history

Forms when silica-rich groundwater fills cavities in volcanic rock, depositing successive chalcedony layers; commonly Cenozoic to older, depending on the host volcanic formation.

Uses & applications

Used for cabochons, carvings, beads, bookends, and decorative specimens; this hand-sized polished piece is mainly a collector/display item.

Geological facts

The curved banding records changing chemistry during repeated silica deposition. Brown coloration typically reflects iron oxides or hydroxides.

Field identification & locations

Identify by concentric or irregularly parallel translucent bands, waxy luster, and resistance to scratching by steel; common sources include Brazil, Uruguay, Mexico, India, Madagascar, and the western United States.