mineral

Limonite (Oxidized Iron Ore)

FeO(OH)·nH2O (Hydrous ferric oxide)

AI-generated identification · may be incorrect

Hardness: 4-5.5 (Mohs), Color: Rusty brown, yellow, earthy orange, Luster: Dull or earthy, Crystal structure: Amorphous (often pseudomorphic after other minerals), Cleavage: None, Specific gravity: 2.7–4.3.

Hardness: 4-5

Identified March 7, 2026More mineral →

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Physical properties

Formation & geological history

Formed by the oxidation and hydration of iron-rich sulfide minerals (like pyrite) in the weathering zone near the Earth's surface. Can be found in gossans ("iron caps") covering ore deposits.

Uses & applications

Historically used as a low-grade iron ore and as a pigment for ochre paints. Today it's primarily of interest to collectors or used as a rough material in landscaping.

Geological facts

Limonite is not a single mineral but a mixture of hydrated iron oxide minerals, mostly goethite. It was one of the earliest pigments used by humans for cave paintings and Neolithic burials.

Field identification & locations

Identify by its distinctive rusty-yellow to brown streak on a porcelain plate and its earthy smell when damp. Commonly found in boggy areas and weathered outcrops. Collectors should look for 'pseudomorphs' where limonite has replaced the shape of pyrite cubes.