mineral

Limonite / Ironstone

Hydrated ferric oxide (FeO(OH)·nH2O)

Hardness: 4.0-5.5; Color: Yellowish-brown to dark brown; Luster: Dull, earthy; Crystal structure: Amorphous; Mohs: 4-5.5; Streak: Yellow-brown.

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

Identified June 22, 2026More mineral →

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Physical properties

Hardness: 4.0-5.5; Color: Yellowish-brown to dark brown; Luster: Dull, earthy; Crystal structure: Amorphous; Mohs: 4-5.5; Streak: Yellow-brown.

Formation & geological history

Formed by the oxidation and hydration of iron-rich sulfide minerals or as a chemical precipitate in shallow marine or swampy environments (bog iron).

Uses & applications

Historically used as a common ore of iron; used as a pigment (brown ochre) in paints; industrial filler.

Geological facts

Limonite is not a true mineral but a mixture of hydrated iron oxide minerals, primarily goethite. It has been used as a pigment by humans for over 30,000 years in cave paintings.

Field identification & locations

Identify in the field by its characteristic yellowish-brown streak on a ceramic plate and its earthy, rusted appearance. Often found in weathered zones of ore deposits.

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Arenite (SiO2 based)

sedimentary

Schist

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Epidote

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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