mineral

Polished banded agate pebble

Chalcedony (microcrystalline quartz, SiO₂), likely agate with iron-oxide staining

AI-generated identification · may be incorrect

Hardness about 6.5–7 Mohs; tan, cream, and gray-black banding with waxy to dull luster. Agate is cryptocrystalline quartz, usually translucent at thin edges, with no obvious cleavage and specific gravity near 2.6.

Identified August 16, 2026More mineral →

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Physical properties

Formation & geological history

Forms when silica-rich groundwater fills cavities in volcanic rock, depositing successive layers of chalcedony; iron and manganese create darker bands. The specimen is likely naturally weathered and subsequently polished, with age depending on its host volcanic rock—commonly Cenozoic to older.

Uses & applications

Used for tumbled stones, cabochons, carvings, bookends, and decorative objects; attractive banded pieces are collectible but generally inexpensive.

Geological facts

Agate banding records changing chemistry and flow conditions during cavity filling. The dark linear feature may be a healed fracture or mineral vein rather than true rhythmic agate banding.

Field identification & locations

Identify by its very hard surface, waxy polish, fine curved or irregular banding, and inability to scratch with a steel knife; it should scratch glass. Common sources include Brazil, Uruguay, Mexico, India, Madagascar, and the western United States.