mineral
Limonite / Ironstone Concretion
Limonite (FeO(OH)·nH2O)
AI-generated identification · may be incorrectHardness 4–5.5 on Mohs scale; dark brown to blackish color with an earthy to submetallic luster, amorphous structure, and yellow-brown streak.
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Physical properties
Hardness 4–5.5 on Mohs scale; dark brown to blackish color with an earthy to submetallic luster, amorphous structure, and yellow-brown streak.
Formation & geological history
Formed via the weathering and hydration of iron-rich minerals such as hematite, pyrite, or siderite in near-surface sedimentary environments.
Uses & applications
Historically mined as an iron ore; currently used as a source of ochre pigments and found in mineral/rockhounding collections.
Geological facts
Limonite is not a true single mineral species, but a mixture of hydrated iron oxides, predominantly goethite.
Field identification & locations
Identified in the field by its dark brown, rough exterior, irregular concretionary or nodular shape, and characteristic rusty-yellow streak.
