mineral

Limonite / Ironstone

Hydrated Iron Oxide (FeO(OH)·nH2O)

AI-generated identification · may be incorrect

Hardness: 4.0 - 5.5 on Mohs scale. Color: Yellowish-brown, reddish-brown, to dark brown. Luster: Earthy, dull, or submetallic. Cleavage: None. Specific Gravity: 2.7 - 4.3. Fracture: Uneven to conchoidal. Streak: Yellow-brown.

Hardness: 4
Color: Yellowish-brown, reddish-brown, to dark brown
Luster: Earthy, dull, or submetallic

Identified July 25, 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, and siderite in near-surface sedimentary environments and weathering zones (gossans).

Uses & applications

Historically used as an important secondary ore of iron and as a natural earth pigment (ochre, raw sienna) for paints and dyes. Primarily of geological interest today.

Geological facts

Limonite is not a true single mineral, but a field term for a mixture of related hydrated iron oxide minerals, primarily goethite and lepidocrocite. It often forms pseudomorphs after other minerals like pyrite, retaining the original crystal shape.

Field identification & locations

Look for a distinct rusty reddish-brown or yellowish-brown coating, earthy texture, and a characteristic yellow-brown streak when scratched against a streak plate. Commonly found in oxidized zones of mineral deposits and iron-rich soils worldwide.