sedimentary
Limonite Geode / Ironstone Concretion
Hydrated iron oxide-hydroxide (FeO(OH)·n H2O)
Hardness: 4-5.5 on the Mohs scale; Color: Brown, yellowish-brown, or ochre; Luster: Submetallic, earthy, or silky; Crystal Structure: Amorphous or microcrystalline (pseudomorphic); Cleavage: None; Specific Gravity: 2.7-4.3
- Hardness
- 4-5
- Color
- Brown, yellowish-brown, or ochre
- Luster
- Submetallic, earthy, or silky
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Physical properties
Hardness: 4-5.5 on the Mohs scale; Color: Brown, yellowish-brown, or ochre; Luster: Submetallic, earthy, or silky; Crystal Structure: Amorphous or microcrystalline (pseudomorphic); Cleavage: None; Specific Gravity: 2.7-4.3
Formation & geological history
Formed through the weathering and oxidation of iron-bearing sulfide minerals or as a concretion in sedimentary iron deposits, often over millions of years.
Uses & applications
Used historically as a source of iron ore, as a pigment (ochre), and collected as a geological specimen by rockhounds.
Geological facts
Limonite is not a single distinct mineral, but rather a mixture of related hydrated iron oxide minerals like goethite, lepidocrocite, and jarosite.
Field identification & locations
Identified by its characteristic yellowish-brown streak, earthy or metallic luster, and hollow concretion structure. Common in weathered iron ore deposits worldwide.
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