mineral

Limonite (Iron Ore)

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

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

Hardness: 4-5

Identified March 1, 2026More mineral →

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Physical properties

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

Formation & geological history

Formed as a secondary mineral through the oxidation and hydration of iron-rich primary minerals (like pyrite or magnetite) in weathered or sedimentary environments.

Uses & applications

A major source of iron ore historicaly; used as an earth pigment (yellow ochre) in paints, and occasionally as a minor construction filler or for geological study.

Geological facts

Limonite is not a true mineral but a mineraloid mixture. It was the primary source of iron in ancient bog-iron processing and is responsible for the yellowish-brown stains on many weathered rock faces.

Field identification & locations

Identify in the field by its distinct 'rusty' yellowish-brown streak; it is often found in bogs, gossans (oxidized outcrop caps), and as a staining agent in sandstone. Found globally in weathering zones.

Other mineral specimens

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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