mineral

Tumbled banded agate

Microcrystalline quartz (SiO₂), chiefly chalcedony

AI-generated identification · may be incorrect

Hardness 6.5–7 Mohs; translucent gray, white, and pink-brown bands with a vitreous-to-waxy luster. It has cryptocrystalline structure, no visible cleavage, conchoidal fracture, and specific gravity about 2.60–2.65.

Identified August 30, 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 over long periods, commonly during the Cenozoic or older volcanic episodes. The specimen has been cut and polished into a tumble.

Uses & applications

Used for cabochons, beads, ornaments, bookends, and lapidary collections; small tumbled pieces are inexpensive decorative stones.

Geological facts

Agate banding reflects changing chemistry, impurities, and growth conditions during cavity filling. The pink coloration may result from iron-bearing impurities or mild dyeing, which cannot be confirmed from the image.

Field identification & locations

Identify by curved or irregular banding, waxy translucency, hardness, and resistance to scratching by steel; glass should not easily scratch it. Common sources include Brazil, Uruguay, India, Mexico, Madagascar, and the United States.