mineral

Polished brown agate/chalcedony pebble

Microcrystalline quartz (SiO₂), likely iron-stained chalcedony or agate

AI-generated identification · may be incorrect

Hardness 6.5–7 Mohs; translucent brown to olive-brown with waxy-to-glassy luster and indistinct microscopic crystal structure. Lacks visible cleavage, has conchoidal fracture, and typically specific gravity near 2.6; the rounded shape indicates tumbling or water wear.

Identified August 30, 2026More mineral →

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Physical properties

Formation & geological history

Silica-rich groundwater deposited cryptocrystalline quartz in cavities or fractures, commonly in volcanic rocks; iron impurities create the brown coloration. Agates formed through repeated silica deposition over millions of years, often during the Cenozoic or older volcanic episodes.

Uses & applications

Used for cabochons, tumbled stones, beads, carvings, and decorative objects; also collected as an affordable lapidary material.

Geological facts

The pale circular marking may be a fortuitous band or inclusion, but the image alone cannot confirm a named variety. Agate commonly displays concentric banding when cut or illuminated from behind.

Field identification & locations

Common in volcanic terrains and river gravels worldwide, especially Brazil, Uruguay, Mexico, India, Madagascar, and the western United States. Test with a steel blade or quartz carefully: genuine chalcedony resists scratching and feels cool, dense, and glassy.