mineral

Limonite (Yellow Ochre)

Limonite (an amorphous mixture of hydrated iron oxides, primarily FeO(OH)·nH2O)

Hardness: 4.0-5.5 (Mohs scale); Color: Yellowish-brown to dark brown; Luster: Dull, earthy; Crystal Structure: Amorphous (non-crystalline); Cleavage: None; Specific Gravity: 2.7-4.3

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

Identified March 30, 2026More mineral →

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Physical properties

Hardness: 4.0-5.5 (Mohs scale); Color: Yellowish-brown to dark brown; Luster: Dull, earthy; Crystal Structure: Amorphous (non-crystalline); Cleavage: None; Specific Gravity: 2.7-4.3

Formation & geological history

Formed as a secondary mineral through the weathering and oxidation of iron-rich minerals such as pyrite, magnetite, or biotite. It is often found in the oxidation zones of ore deposits or as a sedimentary precipitate in bogs (bog iron).

Uses & applications

Historically used as a major iron ore. Today, it is primarily used as a natural pigment (yellow ochre) in paints, dyes, and coatings. It is also a low-value collector's mineral and used in some geological teaching kits.

Geological facts

Limonite has been used by humans as a pigment since the Paleolithic era; it is frequently found in cave paintings across the world. It is not a true mineral species but is considered a mineraloid because it lacks a definite chemical composition and crystal structure.

Field identification & locations

Identify by its characteristic yellowish-brown streak on a porcelain plate and its earthy, dull appearance. It is commonly found in tropical soils (laterites) and near iron-sulfide mines. Collectors look for botryoidal (grape-like) masses or pseudomorphs after other minerals.

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