Where is Iron Oxide Concretions found?
Goethite/Hematite
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Open the appIron Oxide Concretions 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 Concretions
United States
Widespread in sedimentary basins across the US, particularly in states with extensive sandstone and shale formations (e.g., Utah, Colorado, Kansas, Ohio, Pennsylvania). The Navajo Sandstone in Utah is famous for its 'Moqui Marbles' (hematite concretions).
United Kingdom
Common in Jurassic and Cretaceous sedimentary rocks, such as the ironstone beds of the Cleveland Ironstone Formation (Yorkshire) and the Wealden Group (southern England).
Australia
Abundant in various sedimentary sequences, including the Hamersley Basin (Western Australia) where significant iron ore deposits (often concretionary) are found.
Canada
Found in sedimentary rocks across the country, particularly in areas with iron-rich shales and sandstones.
Collecting tips
- Look in Sedimentary Outcrops. Search for concretions in road cuts, stream beds, cliffs, and quarries where sedimentary rocks are exposed. They often weather out of softer host rock and accumulate at the base of slopes.
- Examine Weathered Surfaces. Concretions are typically harder and more resistant to weathering than the surrounding rock, causing them to stand out in relief or be found as loose nodules.
- Check for Iron Staining. The presence of reddish-brown or yellowish-brown staining on host rocks can indicate the presence of iron oxides and potentially concretions.
- Use a Magnet. While goethite is not magnetic, some hematite can be weakly magnetic, especially if it contains minor magnetite. A strong magnet might attract some hematite-rich concretions, though this is not a definitive test for all iron oxides.
Quick Check
- Color:
- Reddish-brown, dark brown, yellowish-brown, or black.
- Luster:
- Dull to earthy, sometimes submetallic.
- Streak:
- Goethite: Yellowish-brown to brownish-yellow. Hematite: Red to reddish-brown.
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