Where is Concretion in Sandstone found?
Sandstone with Iron Oxide Concretion
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Open the appConcretion in Sandstone 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 Concretion in Sandstone
Navajo Sandstone, Utah, USA
Famous for 'Moqui Marbles' (iron oxide concretions) in the Jurassic Navajo Sandstone, particularly in Zion National Park and Grand Staircase-Escalante National Monument.
Dakota Sandstone, Kansas, USA
Known for large, spherical to discoidal ironstone concretions within the Cretaceous Dakota Sandstone.
Badlands National Park, South Dakota, USA
Various concretions, including iron-rich types, are found weathering out of the Oligocene White River Group sediments.
Fossil Butte National Monument, Wyoming, USA
While known for fish fossils, concretions are also present in the Eocene Green River Formation, sometimes preserving organic matter.
Various localities worldwide
Concretions are a common diagenetic feature and can be found in sandstone formations on every continent where suitable conditions for their formation existed.
Collecting tips
- Look for differential weathering. Concretions are often more resistant to erosion than the surrounding host rock, causing them to weather out and accumulate on slopes or at the base of outcrops. They may appear as rounded or oddly shaped 'rocks' on the surface.
- Examine sandstone outcrops. Carefully inspect exposed sandstone layers for spherical, ovoid, or irregular masses that stand out in color or texture from the main rock body. Look for concentric banding or a distinct boundary with the host rock.
- Check for iron staining. The reddish-brown to black color of iron oxide concretions is a key indicator. Look for areas where iron-rich groundwater might have flowed, as this often promotes concretion formation.
- Consider the geological context. Concretions are common in specific sedimentary environments. Researching the local geology and known occurrences of concretions in an area can increase success.
Quick Check
- Color:
- Reddish-brown to black (concretion), variable (sandstone)
- Luster:
- Dull to earthy
- Streak:
- Reddish-brown (for iron oxide concretions)
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