mineral

Tumbled gray chalcedony or quartz pebble

Microcrystalline quartz (SiO₂), possibly gray chalcedony

AI-generated identification · may be incorrect

Smooth, rounded, translucent gray-brown surface with a waxy to dull luster; quartz hardness is about 7 Mohs, lacks visible cleavage, and has a trigonal crystal structure. The appearance is partly obscured by polishing and surface wear.

Identified August 16, 2026More mineral →

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Physical properties

Formation & geological history

Likely a naturally water-worn and/or mechanically tumbled silica-rich pebble, formed from volcanic or sedimentary silica and later weathered. Its precise geological age and locality cannot be determined from the image.

Uses & applications

Used as a decorative stone, pocket specimen, craft material, or inexpensive jewelry component. Common tumbled pieces generally have modest value.

Geological facts

Gray chalcedony can resemble weathered quartzite, flint, or ordinary river stone; translucency at the edges is a useful clue. A quartz-rich specimen should scratch ordinary glass but not be scratched by a steel knife.

Field identification & locations

Common in river gravels and silica-rich volcanic or sedimentary terrains worldwide, including Brazil, Uruguay, India, Madagascar, and the United States. Identification would require hardness, streak, translucency, and ideally a specific-gravity or mineralogical test.