sedimentary

Red Sandstone (River Cobble)

Quartz Arenite / Ferruginous Sandstone

AI-generated identification · may be incorrect

Hardness 6-7, reddish-brown to terracotta color due to iron oxide (hematite) cement, dull to earthy luster, fine to medium-grained clastic sand texture, smooth disk-like stream-rounded shape.

Identified July 24, 2026More sedimentary →

Explore Red Sandstone (River Cobble) in the encyclopedia →

Identify your own rocks.

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

App Store Google Play

Physical properties

Hardness 6-7, reddish-brown to terracotta color due to iron oxide (hematite) cement, dull to earthy luster, fine to medium-grained clastic sand texture, smooth disk-like stream-rounded shape.

Formation & geological history

Formed from the deposition and compaction of quartz sand grains in ancient riverbed, desert dune, or deltaic environments. The red coloration is derived from iron oxide precipitation during diagenesis. Subsequently rounded and smoothed by mechanical stream abrasion over thousands of years.

Uses & applications

Commonly used in landscaping, river rock gardens, masonry building stone, aquariums, and decorative outdoor features.

Geological facts

Smooth, flat river rocks like this were historically prized for skipping stones and shaping into primitive tools or grinding stones due to their symmetrical, water-worn shape.

Field identification & locations

Look for a granular, sandpaper-like texture under magnification with uniform reddish-brown iron staining. Abundant in river valleys, beaches, and glacial gravel deposits globally.