mineral
Limonite/Goethite Iron Concretion
Hydrated iron oxide-hydroxide mixture (FeO(OH)·nH2O)
Hardness: 4-5.5 on the Mohs scale; Color: Yellow-brown, dark brown, to black; Luster: Submetallic, earthy, or silky; Crystal structure: Amorphous to microcrystalline (orthorhombic for goethite); Cleavage: None; Specific gravity: 2.7-4.3
- Hardness
- 4-5
- Color
- Yellow-brown, dark brown, to black
- Luster
- Submetallic, earthy, or silky
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Physical properties
Hardness: 4-5.5 on the Mohs scale; Color: Yellow-brown, dark brown, to black; Luster: Submetallic, earthy, or silky; Crystal structure: Amorphous to microcrystalline (orthorhombic for goethite); Cleavage: None; Specific gravity: 2.7-4.3
Formation & geological history
Formed via the weathering and oxidation of iron-bearing minerals or through chemical/biochemical precipitation in sedimentary environments such as bogs, springs, and shallow marine waters.
Uses & applications
Historically used as a pigment (ochre), a low-grade iron ore, and as a collectible geological specimen.
Geological facts
Limonite is not a true standalone mineral species, but rather a natural mixture of related hydrated iron oxides, most commonly goethite, lepidocrocite, and quartz/clay impurities.
Field identification & locations
Often found in weathered zones of iron ore deposits and sedimentary rock layers worldwide; identified by its characteristic yellowish-brown streak and earthy appearance.
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Limonite / Goethite (Iron Ore Mineral nodule)
FeO(OH)·nH2O / FeO(OH)
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Septarian Pebble
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