Where is Iron Oxide Concretion found?
Goethite/Limonite
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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 and Tertiary sedimentary formations, particularly in states like Kansas, Nebraska, and North Dakota, often weathering out of shales and sandstones.
Eastern United States
Found in various sedimentary units, including the Appalachian Basin, often associated with coal seams or iron-rich shales.
United Kingdom
Common in Jurassic and Cretaceous sedimentary rocks, such as the Cleveland Ironstone Formation and the Wealden Group.
Australia
Widespread in various sedimentary basins, particularly in arid and semi-arid regions where iron-rich soils and sediments are prevalent.
Worldwide
Due to the ubiquitous nature of iron and water, iron oxide concretions can be found in sedimentary environments globally, wherever conditions for their formation are met.
Collecting tips
- Look in Sedimentary Outcrops. Focus on areas with exposed sedimentary rocks, especially sandstones, shales, and siltstones. Concretions often weather out of the softer host rock and accumulate on the surface.
- Check Stream Beds and Beaches. Water erosion can expose and transport concretions. Look in stream beds, riverbanks, and coastal areas where sedimentary rocks are eroding.
- Examine Soil and Alluvial Deposits. In areas with iron-rich soils or recent alluvial deposits, concretions can be found loose on the ground surface or just beneath it.
- Identify Distinct Shapes. Keep an eye out for spherical, discoidal, or irregularly shaped, dense, heavy objects that stand out from the surrounding rock or sediment.
- Perform a Streak Test. A yellowish-brown to reddish-brown streak is characteristic of goethite/limonite and can help differentiate it from other dark minerals.
Quick Check
- Color:
- Yellowish-brown to dark reddish-brown/black
- Luster:
- Earthy to dull, sometimes submetallic
- Streak:
- Yellowish-brown to reddish-brown
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