sedimentary

Bog Iron (Limonite Concretion)

Limonite (FeO(OH)·nH2O)

AI-generated identification · may be incorrect

Hardness: 4-5.5 (Mohs scale); Color: Dark brown to metallic gray with yellowish-orange oxidation; Luster: Sub-metallic to dull/earthy; Structure: Amorphous or microcrystalline; Cleavage: None; Density: 2.7–4.3.

Hardness: 4-5
Color: Dark brown to metallic gray with yellowish-orange oxidation
Luster: Sub-metallic to dull/earthy

Identified June 30, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed by the oxidation of iron-bearing minerals in waterlogged environments such as bogs, swamps, or shallow lakes. Common in glaciated regions of Northern Europe where iron leaches from the soil and precipitates through bacterial action.

Uses & applications

Historically used as a primary source of iron for metallurgy during the Iron Age and Viking Age. Today, it is primarily of geological interest or used as a pigment (ochre).

Geological facts

This specimen was found near Saint Petersburg, Russia, a region historically famous for its bog iron deposits which fueled early industrial iron production in the Russian Empire.

Field identification & locations

Identify by its high density relative to other stones, its typical 'rusty' orange-brown weathering, and its presence in marshy or glaciated lowlands. It often has a pockmarked or bubbly surface texture.