mineral

Tumbled chalcedony or agate pebble

Microcrystalline quartz (SiO₂), likely chalcedony with possible iron-oxide inclusions

AI-generated identification · may be incorrect

Hardness 6.5–7 Mohs; translucent brown to gray, with a waxy-to-glassy luster and no visible cleavage. The rounded shape and smooth surface indicate natural water tumbling or abrasion; internal banding is not clear in the image.

Identified August 10, 2026More mineral →

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Physical properties

Formation & geological history

Forms when silica-rich groundwater fills cavities and fractures in volcanic rocks, precipitating microcrystalline quartz over time; associated host rocks may be Cenozoic or older. The pebble was likely transported and rounded on a beach or in a stream.

Uses & applications

Used for beads, carvings, cabochons, decorative stone, and inexpensive lapidary specimens; attractive banded pieces may be sold as agate.

Geological facts

Chalcedony is a cryptocrystalline quartz aggregate, commonly composed of interlocking fibrous quartz varieties. Brown coloration often comes from iron oxides or hydroxides.

Field identification & locations

Look for waxy luster, translucency at the edges, conchoidal fracture, and quartz hardness; it should scratch ordinary glass but not be scratched by a steel knife. Common worldwide in volcanic terrains and gravel beaches.