mineral
Limonite / Ironstone
Hydrated Iron Oxide (FeO(OH)·nH2O)
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
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Physical properties
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.
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.
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