sedimentary

Rounded brown river cobble

Likely iron-stained quartz-rich sandstone or weathered conglomeratic rock; exact identification requires testing

AI-generated identification · may be incorrect

Hardness likely 6–7 Mohs if quartz-rich; brown, tan, and gray, with dull to slightly granular luster and no obvious cleavage. Rounded shape and surface pitting indicate prolonged abrasion and weathering; specific gravity is likely about 2.5–2.7.

Identified September 17, 2026More sedimentary →

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Physical properties

Formation & geological history

Probably formed as a sedimentary rock from cemented sand or gravel, then rounded by river or beach transport; its age cannot be determined visually. Brown coloration commonly comes from iron-oxide staining.

Uses & applications

Suitable mainly as a collectible or decorative river stone; if confirmed as sandstone, it has limited construction use, but this individual cobble has little commercial value.

Geological facts

The metallic-looking flecks may be mica, iron minerals, or reflective wet grains rather than metal. A white streak or fizzing with dilute acid would help distinguish quartz-rich sandstone from carbonate rock.

Field identification & locations

Common in streambeds and glacial deposits worldwide. Check for a gritty texture, quartz grains, weak/no acid reaction, and whether it scratches glass; a streak test, magnet test, and close inspection of a broken edge would improve identification.