mineral

Polished smoky quartz with chalcedony/agate banding

Quartz (SiO₂), likely microcrystalline quartz (chalcedony) and translucent smoky quartz

AI-generated identification · may be incorrect

Hardness 7 Mohs; brown to gray, translucent, with vitreous to waxy luster and irregular fracture. The rounded surface appears polished or naturally water-worn; visible bands and cloudy zones suggest agate-like chalcedony, though the exact identity cannot be confirmed from one photograph.

Identified August 23, 2026More mineral →

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Physical properties

Formation & geological history

Silica-rich groundwater deposited quartz and chalcedony in cavities or fractures, commonly in volcanic rocks; smoky coloration results from irradiation and trace aluminum. Formation ages range from recent cavity infill to ancient volcanic-hosted deposits.

Uses & applications

Used as a lapidary stone, carving material, cabochons, décor, and collector specimens; generally not used as a structural construction stone.

Geological facts

Quartz is one of Earth’s most abundant minerals and has piezoelectric properties. Agate banding forms through repeated pulses of silica-rich fluid deposition.

Field identification & locations

Look for glassy luster, hardness sufficient to scratch ordinary glass, no obvious cleavage, and curved/conchoidal fracture; chalcedony feels waxier than crystalline quartz. Common sources include Brazil, Uruguay, Mexico, the western United States, and Madagascar.