sedimentary
Ironstone Concretion (Limonite/Goethite)
Ferruginous concretion (Fe2O3·nH2O)
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
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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.
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