sedimentary
Bog Iron (Limonite)
Limonite (Hydrated iron(III) oxide-hydroxide, FeO(OH)·nH2O)
Hardness: 4.0-5.5; Color: Dark brown to yellowish-brown; Luster: Dull to earthy; Crystal Structure: Amorphous; Cleavage: None; Specific Gravity: 2.7-4.3
- Hardness
- 4
- Color
- Dark brown to yellowish-brown
- Luster
- Dull to earthy
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Physical properties
Hardness: 4.0-5.5; Color: Dark brown to yellowish-brown; Luster: Dull to earthy; Crystal Structure: Amorphous; Cleavage: None; Specific Gravity: 2.7-4.3
Formation & geological history
Formed through the chemical or biochemical precipitation of iron oxides from groundwater or stagnant water in swamps, bogs, and wetlands. It is often Holocene in age though can be older.
Uses & applications
Historically used as a major source of iron ore for early metalworking; currently used as a mineral pigment (ochre) and in soil conditioning.
Geological facts
Bog iron was the primary source of iron for Vikings and early American settlers before high-grade hematite and magnetite mines were developed. It is renewable on a human timescale, as it can reform in a bog after being harvested.
Field identification & locations
Identify by its brown-orange streak, earthy texture, and association with wetlands. Common in glaciated areas of Northern Europe and North America. Look for porous, 'rusty' looking masses.
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