mineral

Polished banded agate pebble

Chalcedony (microcrystalline quartz), SiO₂, with iron-oxide or other mineral banding

AI-generated identification · may be incorrect

Hardness 6.5–7 Mohs; gray, black, and cream curved bands; waxy to vitreous luster; cryptocrystalline quartz with no visible cleavage and conchoidal fracture. The smooth surface indicates tumbling or polishing.

Identified August 16, 2026More mineral →

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Physical properties

Formation & geological history

Agate forms when silica-rich groundwater fills cavities in volcanic rock, depositing successive layers over time; individual specimens may range from millions to hundreds of millions of years old. Common sources include Brazil, Uruguay, Mexico, India, Madagascar, and the United States.

Uses & applications

Used for cabochons, beads, carvings, paperweights, and decorative objects; thin slices are used in jewelry and ornament. This small polished piece has modest commercial value.

Geological facts

The banding records changing chemistry, temperature, and fluid conditions during cavity filling. Its dark color may reflect manganese- or iron-bearing inclusions, though dyeing cannot be ruled out from the image alone.

Field identification & locations

Identify by its curved parallel bands, translucent edges, waxy polish, and quartz-like hardness; it should scratch glass but not be scratched by steel easily. Test cautiously, since a polished specimen may be coated or treated.