mineral

Limonite / Goethite pseudomorph

Hydrated Iron Oxide (FeO(OH)·nH2O)

AI-generated identification · may be incorrect

Hardness: 4.0 - 5.5 on Mohs scale. Color: Yellowish-brown, dark brown, or blackish. Luster: Earthy, sub-metallic, or dull. Specific gravity: 2.7 - 4.3. Crystal structure: Amorphous or fine-grained massive aggregates.

Hardness: 4
Color: Yellowish-brown, dark brown, or blackish
Luster: Earthy, sub-metallic, or dull

Identified July 27, 2026More mineral →

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Physical properties

Formation & geological history

Formed through the weathering and oxidation of iron-rich primary minerals such as pyrite, marcasite, magnetite, or siderite in near-surface aqueous conditions.

Uses & applications

Historically used as a major iron ore and as a natural pigment (yellow ochre and brown umber). Also collected as mineral specimens.

Geological facts

Limonite is not a true single mineral but a mixture of hydrated iron oxides, predominantly goethite. It often forms perfect pseudomorphs replacing cubic pyrite crystals, resulting in 'iron cross' or cubic rust formations.

Field identification & locations

Identified by its distinctive yellowish-brown streak, rusty earthy appearance, and lack of magnetism compared to magnetite. Commonly found in oxidized zones of ore deposits worldwide.