gemstone

Tumbled brown banded agate

Chalcedony (microcrystalline quartz), SiO₂, with iron-oxide inclusions

AI-generated identification · may be incorrect

Hardness 6.5–7 Mohs; waxy to vitreous luster; translucent brown, gray, and cream banding; cryptocrystalline quartz with no visible cleavage and conchoidal fracture. The smooth surface indicates mechanical tumbling and polishing.

Identified August 23, 2026More gemstone →

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Physical properties

Formation & geological history

Agate forms when silica-rich groundwater fills cavities in volcanic rock, depositing successive layers of chalcedony and quartz, often over millions of years. Iron and other impurities create the brown coloration and banding.

Uses & applications

Used for cabochons, beads, carvings, ornaments, and lapidary collections; durable enough for small decorative objects but generally not high-value jewelry.

Geological facts

Agate is a variety of chalcedony distinguished by internal banding or patterned zoning. Its appearance can resemble jasper or dyed chalcedony, so exact identification may require examination of translucency and bands.

Field identification & locations

Common sources include Brazil, Uruguay, India, Madagascar, Mexico, and the western United States. Field clues are waxy luster, fine banding, translucence at thin edges, and hardness sufficient to scratch glass.