mineral
Limonite or Ironstone
Hydrated iron oxide-hydroxide, approximately FeO(OH)·n(H2O)
Hardness: 4-5.5 on the Mohs scale; Color: Yellow-brown, dark brown, to blackish; Luster: Earthy, submetallic, or silky; Crystal structure: Amorphous or microcrystalline, typically forms as stalactitic, mammillary, or massive crusts; Cleavage: None; Specific Gravity: 2.7-4.3
- Hardness
- 4-5
- Color
- Yellow-brown, dark brown, to blackish
- Luster
- Earthy, submetallic, or silky
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Physical properties
Hardness: 4-5.5 on the Mohs scale; Color: Yellow-brown, dark brown, to blackish; Luster: Earthy, submetallic, or silky; Crystal structure: Amorphous or microcrystalline, typically forms as stalactitic, mammillary, or massive crusts; Cleavage: None; Specific Gravity: 2.7-4.3
Formation & geological history
Formed as a secondary mineral resulting from the oxidation and weathering of various iron-bearing minerals, commonly occurring in gossans (iron hats), bog iron deposits, and sedimentary iron ores.
Uses & applications
Historically used as an iron ore, a yellow-brown pigment (ochre) in paints, and occasionally cut into cabochons or collected by mineral enthusiasts.
Geological facts
Limonite is not a true distinct mineral species, but rather a mixture of related hydrated iron oxides, most commonly goethite, lepidocrocite, and jarosite.
Field identification & locations
Easily identified by its characteristic yellowish-brown streak on an unglazed porcelain plate. Found worldwide, especially in weathered iron deposits and oxidizing zones of sulfide ore bodies.
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Arenite (SiO2 based)
sedimentary
Soil with Mineral Detritus and Quartz Fragments
Regolith / Silicate Mineral Aggregate
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Limonite / Goethite (Iron Ore Mineral nodule)
FeO(OH)·nH2O / FeO(OH)
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Septarian Pebble
Septarian nodule / Concretion
sedimentary
Schist
Schist
Metamorphic
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Orthoclase (KAlSi3O8)
mineral