mineral

Limonite (Iron Ore/Bog Iron)

Hydrated Iron(III) Oxide-Hydroxide (FeO(OH)·nH2O)

Hardness: 4 to 5.5 on Mohs scale; Color: Yellowish-brown to dark brown; Luster: Dull, earthy; Crystal structure: Amorphous; Cleavage: None; Specific Gravity: 2.7 to 4.3

Hardness: 4 to 5
Color: Yellowish-brown to dark brown
Luster: Dull, earthy

Identified May 17, 2026More mineral →

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Physical properties

Hardness: 4 to 5.5 on Mohs scale; Color: Yellowish-brown to dark brown; Luster: Dull, earthy; Crystal structure: Amorphous; Cleavage: None; Specific Gravity: 2.7 to 4.3

Formation & geological history

Forms as a secondary mineral through the weathering and oxidation of other iron-rich minerals (like pyrite or magnetite) or as a chemical precipitate in marshy, swampy environments (bog iron).

Uses & applications

Historically used as a major source of iron ore and as a source of yellow pigments (yellow ochre). Today, it is mostly a minor iron ore and a mineral for geological studying.

Geological facts

Limonite is not a true mineral in the strict sense but a mixture of hydrated iron oxide minerals. It was the primary source of iron for thousands of years before more efficient mining methods were developed for hematite.

Field identification & locations

Identify in the field by its characteristic yellowish-brown streak on a porcelain plate and its earthy, rusted appearance. Often found in mineralized zones or swampy deposits.

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