mineral
Limonite (Goethite/Ironstone)
Hydrated iron oxide-hydroxide, approximately FeO(OH)·nH2O
Hardness: 4 to 5.5 on the Mohs scale. Color: Yellowish-brown, dark brown, reddish-brown, to ochre yellow. Luster: Submetallic, earthy, or dull. Crystal Structure: Amorphous or microcrystalline (pseudomorphic after other minerals). Cleavage: None. Specific Gravity: 2.7 to 4.3.
- Hardness
- 4 to 5
- Color
- Yellowish-brown, dark brown, reddish-brown, to ochre yellow
- Luster
- Submetallic, earthy, or dull
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Physical properties
Hardness: 4 to 5.5 on the Mohs scale. Color: Yellowish-brown, dark brown, reddish-brown, to ochre yellow. Luster: Submetallic, earthy, or dull. Crystal Structure: Amorphous or microcrystalline (pseudomorphic after other minerals). Cleavage: None. Specific Gravity: 2.7 to 4.3.
Formation & geological history
Formed through the secondary weathering and oxidation of primary iron-bearing minerals (like pyrite, magnetite, or siderite) in low-temperature environments, often found in gossans and sedimentary bog iron deposits.
Uses & applications
Historically used as a pigment (yellow ocher), an ore for low-grade iron production, and collected by rockhounds and mineral enthusiasts.
Geological facts
Limonite is not a true standalone mineral species, but rather a mixture of related hydrated iron oxides, most commonly goethite and lepidocrocite. It has been used by humans as a pigment since prehistoric cave paintings.
Field identification & locations
Easily identified by its characteristic yellowish-brown to reddish-brown streak on an unglazed porcelain plate. Found worldwide in weathered iron deposits, soils, and sedimentary rock formations.
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Limonite / Goethite (Iron Ore Mineral nodule)
FeO(OH)·nH2O / FeO(OH)
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Septarian Pebble
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