mineral

Limonite (Iron Ore)

FeO(OH)·nH2O (Hydrated iron(III) oxide-hydroxide)

Hardness: 4-5.5; Color: Yellowish-brown to dark brown; Luster: Dull, earthy; Crystal Structure: Amorphous or microcrystalline; Cleavage: None; Specific Gravity: 2.7-4.3.

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

Identified March 1, 2026More mineral →

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Physical properties

Hardness: 4-5.5; Color: Yellowish-brown to dark brown; Luster: Dull, earthy; Crystal Structure: Amorphous or microcrystalline; Cleavage: None; Specific Gravity: 2.7-4.3.

Formation & geological history

Formed primarily from the chemical weathering of iron-rich minerals such as pyrite, magnetite, and hematite in oxidation zones. Often found in marshes (bog iron) or as a staining agent in sedimentary rock layers.

Uses & applications

Historically used as an iron ore and as a source of pigment (yellow ochre). Today, it is used mostly in industrial pigments and as a minor source of iron.

Geological facts

Limonite is not a single mineral but a mixture of hydrated iron oxides. It was a primary source of iron for early civilizations and was used by ancient artists to create cave paintings.

Field identification & locations

Identify by its characteristic yellowish-brown streak on a porcelain plate and high density relative to other dull rocks. Commonly found in gossans (iron caps over ore deposits) and sedimentary basins.

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