mineral

Limonite (Oxidized Iron Ore)

FeO(OH)·nH2O (Hydrous ferric oxide)

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.

Other mineral specimens

See all

Sandstone (with potential mineral staining/concretions)

Arenite (SiO2 based)

sedimentary

Epidote

Epidote | Ca2(Al2,Fe3+)(SiO4)(Si2O7)O(OH)

metamorphic

Nephrite Jade

Nephrite

Mineral/Rock

Banded Gneiss (River Rock/Pebble)

Gneiss (specifically a banded variety often found as a river rock)

Metamorphic Rock

Green Apatite on Albite

Fluorapatite [Ca5(PO4)3F] on Albite [Na(AlSi3O8)]

mineral

Epidote

Epidote - Ca2(Al2,Fe3+)3(SiO4)3(OH)

mineral