sedimentary

Ferruginous Sandstone (Ironstone Nodules)

Ferruginous Sandstone with Limonite/Goethite coating (Fe2O3·H2O)

AI-generated identification · may be incorrect

Hardness: 6-7 (Mohs scale) for the silica base; Color: Reddish-brown, tan, and gray; Luster: Dull/Earthy; Structure: Clastic, granular texture; Cleavage: None; Specific Gravity: 2.5-3.0

Hardness: 6-7 (Mohs scale) for the silica base
Color: Reddish-brown, tan, and gray
Luster: Dull/Earthy

Identified February 14, 2026More sedimentary →

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Physical properties

Hardness: 6-7 (Mohs scale) for the silica base; Color: Reddish-brown, tan, and gray; Luster: Dull/Earthy; Structure: Clastic, granular texture; Cleavage: None; Specific Gravity: 2.5-3.0

Formation & geological history

Formed through the accumulation and dewatering of sand-sized minerals (mostly quartz) in riverbeds or marine environments, then cemented together by iron oxide minerals precipitated from groundwater. This specific specimen shows weathering in an oxidizing environment.

Uses & applications

Commonly used as a base material in construction, road fill, and occasionally as a low-grade iron ore. In the lapidary world, it is sometimes used for yard decoration or rustic stone carving.

Geological facts

The reddish-brown color is essentially 'geological rust'. These rocks are often formed into 'Moki Marbles' or 'Concretions' that can have unusual spherical or layered shapes, leading people to mistake them for fossils or meteorites.

Field identification & locations

Identify by its gritty texture and characteristic orange-brown 'rust' staining. It will not scratch with a copper penny but will usually be scratched by a steel file. Commonly found in deserts or river banks in the American Southwest and worldwide.