Where is Ironstone Concretion found?
Iron oxide-cemented sandstone/siltstone
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Open the appIronstone 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 Ironstone Concretion
United States
Widely distributed in sedimentary basins across the US, including the Colorado Plateau (e.g., Utah, Arizona), where they are often associated with Mesozoic sandstones, and in various Cenozoic sedimentary formations.
United Kingdom
Common in Jurassic and Cretaceous sedimentary sequences, particularly in the Wealden Group and various ironstone formations.
Canada
Found in numerous sedimentary successions, including those in the Western Canada Sedimentary Basin.
Australia
Present in various sedimentary units, often associated with lateritic weathering profiles and ancient fluvial deposits.
Collecting tips
- Look for resistant features. Ironstone concretions are often more resistant to weathering than the surrounding host rock, causing them to stand out as knobs, spheres, or irregular masses on eroded surfaces, stream beds, or cliff faces.
- Check for color contrast. Their characteristic reddish-brown to dark brown color often contrasts with lighter-colored sandstones or siltstones.
- Examine eroded areas. Riverbanks, road cuts, quarries, and coastal cliffs are excellent places to find concretions that have been exposed by erosion.
- Note spherical or discoidal shapes. While not exclusively spherical, many concretions exhibit distinct, often symmetrical, rounded forms that differentiate them from typical rock fragments.
Quick Check
- Color:
- Reddish-brown to dark brown
- Luster:
- Dull to earthy
- Streak:
- Reddish-brown (for hematite-rich) or yellowish-brown (for goethite-rich)
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