sedimentary

Sandstone with Ironstone Concretion

Arenite with Hematite/Goethite nodules (Fe2O3 / FeO(OH))

AI-generated identification · may be incorrect

Hardness: 6.5-7 (sandstone matrix), 5-6 (ironstone); Color: Tan/buff matrix with dark brown/rusty inclusions; Luster: Dull/Earthy; Crystal structure: Granular/Amorphous; Specific gravity: 2.2-2.8

Hardness: 6
Color: Tan/buff matrix with dark brown/rusty inclusions
Luster: Dull/Earthy

Identified March 7, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7 (sandstone matrix), 5-6 (ironstone); Color: Tan/buff matrix with dark brown/rusty inclusions; Luster: Dull/Earthy; Crystal structure: Granular/Amorphous; Specific gravity: 2.2-2.8

Formation & geological history

Formed through the lithification of sand particles, where groundwater rich in dissolved iron precipitated minerals in the pore spaces, creating hard, iron-rich nodules known as concretions or 'ironstone' within the softer host rock.

Uses & applications

Primarily used as construction material (building stone), landscaping, and as a geological curiositiy for collectors interested in sedimentary structures.

Geological facts

These are often mistaken for fossils or meteorites due to their odd shapes and dark, metallic appearance. Large-scale versions are sometimes called 'Moqui marbles' or 'shaman stones' in the American Southwest.

Field identification & locations

Identify in the field by the distinct color contrast and the fact that the dark spots are harder and more resistant to weathering than the surrounding rock. Found globally in ancient riverbeds and desert environments.