sedimentary

Rounded sandstone cobble

Quartz-rich sandstone, likely arkosic or ferruginous sandstone

AI-generated identification · may be incorrect

Typically Mohs hardness 6–7 for quartz grains, with tan-brown color, dull to earthy luster, and a fine granular texture; iron oxides cause the rusty coloration. It appears water-rounded and may be moderately porous, with no obvious cleavage.

Identified September 5, 2026More sedimentary →

Explore Rounded sandstone cobble in the encyclopedia →

Identify your own rocks.

Get a report just like this from any photo, free.

App Store Google Play

Physical properties

Formation & geological history

Formed when sand-sized grains—mainly quartz with possible feldspar—were compacted and cemented, likely during a Mesozoic or Cenozoic sedimentary episode; its smooth shape developed through stream or beach transport. Exact age and composition require thin-section or chemical testing.

Uses & applications

Common sandstone is used as building stone, aggregate, paving material, and occasionally as a decorative or educational specimen; this ordinary cobble has little jewelry value.

Geological facts

The dark speckles may be iron-oxide staining, lithic fragments, or minor mafic minerals. A streak, acid, hardness, and grain-size examination can distinguish sandstone from weathered volcanic rock.

Field identification & locations

Look for visible sand grains, gritty texture, and layered or porous broken surfaces; common in riverbeds, beaches, and sedimentary terrains worldwide. A steel nail may scratch softer cement, while quartz grains resist scratching.