sedimentary

Ironstone Concretion (Limonite/Goethite)

Ferruginous concretion (Fe2O3·nH2O)

AI-generated identification · may be incorrect

Hardness: 4-5.5; Color: Dark brown to blackish; Luster: Dull to sub-metallic; Structure: Massively amorphous/microcrystalline; Cleavage: None; SG: 3.3-4.3

Hardness: 4-5
Color: Dark brown to blackish
Luster: Dull to sub-metallic

Identified June 15, 2026More sedimentary →

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Physical properties

Hardness: 4-5.5; Color: Dark brown to blackish; Luster: Dull to sub-metallic; Structure: Massively amorphous/microcrystalline; Cleavage: None; SG: 3.3-4.3

Formation & geological history

Formed through the precipitation of iron oxide minerals within the pore spaces of sedimentary layers (such as sandstone or shale). These often form in arid or semi-arid environments following chemical weathering.

Uses & applications

Primarily used as an ore of iron in industrial settings; sometimes used in jewelry as beads or kept as geological curiosities for their spherical shape.

Geological facts

Commonly known as 'Moqui marbles' or 'iron nuts,' these specimens are often mistaken for meteorites due to their heavy weight, dark color, and spherical shape. The location provided (Somaliland/Ethiopia border) is geologically consistent with ironstone-rich sedimentary formations.

Field identification & locations

Identify by its high density compared to normal rocks, a yellowish-brown streak on a ceramic plate, and lack of magnetism (unlike magnetite). Common in desert plateaus.