sedimentary

Rounded sandstone cobble

Clastic sandstone, likely quartz-rich (quartz arenite or arkose)

AI-generated identification · may be incorrect

Fine- to medium-grained, tan-gray, dull to slightly sparkly surface with rounded abrasion; chiefly quartz and feldspar cemented by silica, iron oxides, or carbonate. Typical hardness is about 6–7 for grains, with no obvious cleavage; specific gravity roughly 2.2–2.7.

Identified September 5, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed when sand accumulated, compacted, and cemented in a former river, beach, dune, or shallow-marine environment, then rounded by transport. Its exact geological age cannot be determined from the photograph.

Uses & applications

Used as aggregate, building stone, paving, and occasionally decorative stone; this ordinary cobble has little commercial or collector value.

Geological facts

The smooth elongated shape reflects prolonged abrasion in flowing water or surf. A fresh broken surface would reveal visible sand grains and may fizz weakly with dilute hydrochloric acid if carbonate-cemented.

Field identification & locations

Common worldwide in river gravels and sedimentary outcrops. Confirm with a hand lens, grain-size inspection, streak (usually white), and acid test; it is unlikely to be a meteorite because of its granular, non-metallic appearance.