sedimentary

Likely iron-rich sandstone or ironstone pebble

Ferruginous sandstone (quartz-rich sandstone cemented by iron oxides); exact identification requires testing

AI-generated identification · may be incorrect

Dark reddish-brown, fine-grained and matte, with a granular surface; likely dominated by quartz and hematite/goethite. Typical quartz hardness is Mohs 7, but cement and grain size affect the specimen’s overall hardness; crystal structure is not visible.

Identified September 30, 2026More sedimentary →

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Physical properties

Formation & geological history

Likely formed as sand deposited in a sedimentary setting and later cemented by iron oxides. Its age and original environment cannot be determined from the photograph.

Uses & applications

Common ferruginous sandstone is mainly of geological or collecting interest; sandstone more broadly is used as building stone and aggregate.

Geological facts

Iron oxides give many sandstones their rusty red-brown coloration. The rounded, smoothed shape suggests natural abrasion, possibly in a stream or on a beach.

Field identification & locations

Look for gritty grains, reddish-brown iron staining, and a lack of metallic luster; a streak or hardness test can help distinguish it from other dark pebbles. Ferruginous sandstone occurs worldwide wherever iron-rich sedimentary rocks are exposed.