sedimentary
Limonite Concretion
Goethite/Limonite (FeO(OH)·nH2O)
Hardness: 4-5.5 (Mohs scale), Color: Brownish-yellow to dark brown, Luster: Dull/Earthy, Crystal Structure: Amorphous or cryptocrystalline, Cleavage: None, Specific Gravity: 2.7-4.3
- Hardness
- 4-5
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Physical properties
Hardness: 4-5.5 (Mohs scale), Color: Brownish-yellow to dark brown, Luster: Dull/Earthy, Crystal Structure: Amorphous or cryptocrystalline, Cleavage: None, Specific Gravity: 2.7-4.3
Formation & geological history
Formed by the precipitation of iron oxide minerals from groundwater within sedimentary rock layers, often around a nucleus. They can range from the Cretaceous to the Holocene period.
Uses & applications
Primarily used as a minor ore of iron; also used as an ocher pigment and for educational geological collections.
Geological facts
Commonly known as 'bog iron' when found in marshes. Some hollow varieties are called 'rattle stones' because a smaller loose pebble may be trapped inside.
Field identification & locations
Identify by its heavy weight relative to size and yellowish-brown streak. Common in sandstone or clay-rich soil. Look for spherical or potato-like shapes with a distinct weathered rind.
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