sedimentary
Ironstone (Limonitic Concretion)
Limonite (FeO(OH)·nH2O) with Goethite and Hematite inclusions
Hardness: 4-5.5 (Mohs scale); Color: Yellowish-brown to dark reddish-brown; Luster: Dull to earthy; Crystal Structure: Amorphous/microcrystalline; Specific Gravity: 2.7-4.3
- Hardness
- 4-5
- Color
- Yellowish-brown to dark reddish-brown
- Luster
- Dull to earthy
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Physical properties
Hardness: 4-5.5 (Mohs scale); Color: Yellowish-brown to dark reddish-brown; Luster: Dull to earthy; Crystal Structure: Amorphous/microcrystalline; Specific Gravity: 2.7-4.3
Formation & geological history
Formed through the chemical precipitation of iron-rich minerals in sedimentary basins or as bog iron, often occurring during the Cenozoic or Mesozoic eras. It commonly forms around a nucleus within sandstone or shale beds.
Uses & applications
Historically used as a low-grade iron ore; currently used as a pigment (ochre), in landscaping, and as decorative stone for rock gardens.
Geological facts
Ironstones often form distinctive 'rattle stones' where a loose core creates sound when shaken. Large deposits in England fueled the early Industrial Revolution's iron production.
Field identification & locations
Identify by its high density relative to other sedimentary rocks and its characteristic rusty streak. Commonly found in deserts (desert varnish) or eroded creek beds. High concentration of iron makes it feel unexpectedly heavy.
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