sedimentary
Ironstone (Limonite/Hematite)
Ferruginous sedimentary rock (Fe2O3·nH2O / Fe2O3)
Hardness: 4-5.5 on Mohs scale; Color: Rusty brown, reddish-orange, earthy yellow; Luster: Dull to earthy; Crystal Structure: Amorphous or microcrystalline; Cleavage: None; Specific Gravity: 3.3-4.3
- Hardness
- 4-5
- Color
- Rusty brown, reddish-orange, earthy yellow
- Luster
- Dull to earthy
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Physical properties
Hardness: 4-5.5 on Mohs scale; Color: Rusty brown, reddish-orange, earthy yellow; Luster: Dull to earthy; Crystal Structure: Amorphous or microcrystalline; Cleavage: None; Specific Gravity: 3.3-4.3
Formation & geological history
Formed by the chemical precipitation of iron minerals in marine or swampy environments, or by the oxidation of iron-rich minerals in soil. Often associated with the Phanerozoic eon.
Uses & applications
Historically used as iron ore. Today used primarily as an industrial pigment (ochre), in landscaping, and as a collector's specimen.
Geological facts
Ironstone is what gives many 'Red Rocks' parks their color. It often forms 'concretions' which can be mistaken for fossils or meteorites due to their weight and appearance.
Field identification & locations
Identify by its heavy weight (relative to other rocks), rusty streak, and lack of magnetism (unlike magnetite). Common in coal-bearing areas and desert regions.
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