sedimentary
Limonite Geode (Ironstone Concretion)
Goethite/Limonite FeO(OH)·nH2O
Hardness: 4 to 5.5 (Mohs), Color: Dark brown to yellowish-red/ochre, Luster: Dull to earthy, Crystal Structure: Amorphous/Microcrystalline, Specific Gravity: 2.7 to 4.3
- Hardness
- 4 to 5
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Physical properties
Hardness: 4 to 5.5 (Mohs), Color: Dark brown to yellowish-red/ochre, Luster: Dull to earthy, Crystal Structure: Amorphous/Microcrystalline, Specific Gravity: 2.7 to 4.3
Formation & geological history
Formed by the chemical precipitation of iron-rich minerals in soil or sedimentary rock layers, often around a biological nucleus or through the oxidation of iron ores. Frequently found in boggy environments or weathering zones.
Uses & applications
Historically used as a source of iron ore and as a pigment (brown ochre). For collectors, they are kept as interesting geological curiosities or 'rattle stones' if they contain loose sand or pebbles.
Geological facts
Limonite is not a single mineral but a mixture of hydrated iron oxide minerals. When these form hollow shells, they are sometimes known as 'eagle stones' or 'etites' in folklore, once believed to assist in childbirth.
Field identification & locations
Identified by its heavy weight relative to size (high iron content), rusty streaks, and frequent hollow-centered concretionary shape. Commonly found in areas with high iron concentrations in the groundwater.
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