Where is Iron Oxide Concretion found?
Limonite/Goethite Concretion
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Open the appIron Oxide Concretion occurs in specific geological environments. Knowing where to look, and in what kind of rock, is the difference between going home empty-handed and finding a great specimen.
Where to find Iron Oxide Concretion
Midwestern United States
Abundant in Cretaceous sandstones (e.g., Dakota Formation) and shales, often weathering out as 'cannonball' concretions.
Eastern United States
Common in various sedimentary units, particularly in coastal plain sediments and bog iron deposits.
Europe
Found in numerous sedimentary basins, including Jurassic and Cretaceous formations in the UK, France, and Germany.
Australia
Present in lateritic soils and weathered sedimentary rocks, particularly in arid and semi-arid regions.
Globally
Due to the ubiquitous nature of iron and water, iron oxide concretions can be found in sedimentary environments worldwide.
Collecting tips
- Look in Sedimentary Outcrops. Examine road cuts, river banks, and cliffs composed of sandstones, shales, and siltstones. Concretions are often harder than the surrounding rock and may weather out and accumulate at the base of outcrops.
- Check for Erosion. Areas undergoing active erosion, such as stream beds or coastal bluffs, can expose concretions that have been released from their host rock.
- Identify Iron Staining. The presence of reddish-brown or yellowish-brown staining on rocks or in soils can indicate the presence of iron oxides and potentially concretions.
- Examine Boggy Areas. For 'bog iron' concretions, look in wetlands, swamps, and bogs where iron-rich groundwater emerges and oxidizes.
Quick Check
- Color:
- Brown, yellow, reddish-brown
- Luster:
- Dull, earthy, submetallic
- Streak:
- Yellowish-brown to brownish-yellow (for limonite/goethite)
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