sedimentary

Bog Iron / Limonite Concretion

Goethite/Limonite mixture (FeO(OH)·nH2O)

AI-generated identification · may be incorrect

Hardness: 4.0-5.5 (Mohs scale); Color: Dark brown to black with yellowish-orange weathering; Luster: Dull, earthy, to sub-metallic; Crystal Structure: Amorphous or microcrystalline; Specific Gravity: 2.7-4.3

Hardness: 4
Color: Dark brown to black with yellowish-orange weathering
Luster: Dull, earthy, to sub-metallic

Identified March 29, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the oxidation and precipitation of iron-bearing minerals in wetlands, shallow water, or through the leaching of iron-rich soils. Often found in Quaternary to modern environments, as well as older sedimentary beds.

Uses & applications

Historically used as a major source of iron for early smelting (especially during the Viking Age and colonial era), pigment (ochre), and occasionally as a low-grade construction aggregate.

Geological facts

Bog iron was the primary source of iron for European civilizations before the advent of deep mining. These formations are renewable in geological terms, as iron-oxidizing bacteria can precipitate new deposits in wetlands over decades rather than millions of years.

Field identification & locations

Identify by its heavy weight relative to surrounding rocks, distinct rusty-orange streak when scratched on porcelain, and porous/vesicular texture. Commonly found in streambeds, marshes, and glaciated regions with high iron groundwater.