mineral

Limonite (Iron Ore)

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

Hardness: 4.0-5.5 on Mohs scale; Color: Yellowish-brown to dark brown; Luster: Dull to earthy; Crystal Structure: Amorphous (no definite crystal form); Streak: Yellow-brown; Specific Gravity: 2.7-4.3.

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

Identified June 19, 2026More mineral →

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Physical properties

Formation & geological history

Formed usually by the oxidation and hydration of iron-rich sulfide minerals (like pyrite) or the weathering of other iron-rich rocks. It often occurs as a secondary mineral in the oxidation zones of ore deposits.

Uses & applications

Historically used as an Important iron ore. Today, it is primarily used as a pigment (ocher) for paints, dyes, and concrete, and as a soil conditioner.

Geological facts

Limonite is not a true mineral in the modern sense but a mixture of related hydrated iron oxide minerals, mostly goethite. It has been used by humans as a pigment since prehistoric times, found in cave paintings worldwide.

Field identification & locations

Identify by its characteristic yellowish-brown streak on a porcelain plate and its rusty, earthy appearance. It often forms 'gossans' or iron caps over mineral veins. Commonly found in bog deposits or weathered outcrops.

Other mineral specimens

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Sandstone (with potential mineral staining/concretions)

Arenite (SiO2 based)

sedimentary

Schist

Metamorphic

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