sedimentary
Ironstone (Limonite/Hematite)
Ferruginous Sedimentary Rock (composed largely of Fe2O3 and FeO(OH)·nH2O)
Hardness: 4.0-5.5 on Mohs scale; Color: Reddish-brown, dark brown, to yellowish-orange; Luster: Dull to sub-metallic; Structure: Often massive, oolitic, or concretionary; Specific Gravity: 3.3-4.3.
- Hardness
- 4
- Color
- Reddish-brown, dark brown, to yellowish-orange
- Luster
- Dull to sub-metallic
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Physical properties
Hardness: 4.0-5.5 on Mohs scale; Color: Reddish-brown, dark brown, to yellowish-orange; Luster: Dull to sub-metallic; Structure: Often massive, oolitic, or concretionary; Specific Gravity: 3.3-4.3.
Formation & geological history
Formed by the chemical precipitation of iron minerals from solution in sedimentary environments, often in shallow marine or freshwater bog conditions. Ages range from Precambrian to modern times.
Uses & applications
Historical source of iron ore for smelting; currently used as road base, decorative landscape stone, and sometimes as a pigment (ochre).
Geological facts
Ironstone concretions can sometimes contain fossils in their centers. The iron within these rocks is what gives much of the Earth's soil its characteristic red or orange color.
Field identification & locations
Identify by its high density (feels heavy for its size) and the reddish stain it leaves on hands or streak plates. Look for 'rust' like appearance in sedimentary layers.
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