Where is Sandstone Concretion found?
Sedimentary rock, likely iron-rich sandstone
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Open the appSandstone 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 Sandstone Concretion
Badlands National Park, South Dakota, USA
Known for abundant and diverse concretions, including sandstone concretions, often exposed by erosion.
The Moeraki Boulders, New Zealand
Famous for large, spherical septarian concretions, which are a type of concretion formed in mudstone, but illustrate the scale and form concretions can take.
The Te Paki Giant's Playground, New Zealand
Features large, spherical sandstone concretions exposed on beaches.
The Bardenas Reales, Navarre, Spain
Erosional landscapes expose numerous concretions within sandstone and mudstone layers.
Various desert environments (e.g., Utah, Arizona, USA)
Often found in arid regions where wind and water erosion expose sedimentary layers, revealing concretions that are more resistant to weathering.
Collecting tips
- Look for Differential Erosion. Concretions are typically harder than the surrounding host rock. Look for areas where erosion has preferentially removed softer sediments, leaving the more resistant concretions exposed or protruding.
- Examine Sedimentary Outcrops. Focus on road cuts, river banks, cliffs, and badlands where sedimentary layers are well-exposed. Concretions often weather out and accumulate at the base of slopes.
- Check for Spherical or Ovoid Shapes. While not all concretions are perfectly spherical, their distinct, often rounded shapes are a key indicator. Look for these anomalous forms within otherwise bedded sedimentary rocks.
- Note Color Contrasts. Iron-rich concretions often stand out due to their darker, reddish-brown to black colors against lighter-colored sandstones.
- Investigate Weathered Surfaces. Concretions can sometimes be identified by their distinct texture or hardness when examining weathered rock surfaces. Tapping with a rock hammer might produce a different sound than the host rock.
Quick Check
- Color:
- Reddish-brown, dark brown, yellowish-brown, black, or sometimes gray/tan.
- Luster:
- Dull to earthy.
- Streak:
- Varies depending on cementing material; iron-rich concretions may have a reddish-brown streak (hematite) or yellowish-brown streak (goethite/limonite). Calcite-cemented concretions will have a white streak.
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