Where is Sandstone concretion found?
Sandstone concretion
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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
Theodore Roosevelt National Park, North Dakota, USA
Known for abundant 'cannonball' concretions weathering out of the Paleocene Sentinel Butte Formation.
Moeraki Boulders, New Zealand
Large, spherical concretions (septarian concretions) found on Koekohe Beach, formed in Paleocene mudstone.
Bowling Ball Beach, Mendocino County, California, USA
Features numerous spherical concretions exposed on the beach, weathering out of Miocene mudstone and sandstone.
Bisti/De-Na-Zin Wilderness, New Mexico, USA
Contains numerous bizarrely shaped sandstone concretions and hoodoos in the Cretaceous Kirtland and Fruitland Formations.
Utah and Colorado Plateaus, USA
Commonly found in various Mesozoic sandstone formations (e.g., Navajo Sandstone, Entrada Sandstone) where they contribute to unique erosional features.
Collecting tips
- Look for Differential Erosion. Concretions are typically harder and more resistant to erosion than the surrounding host rock. Look for them weathering out of cliffs, stream banks, or exposed bedrock, often forming prominent knobs, spheres, or odd shapes.
- Examine Sandstone Outcrops. Focus on areas where sandstone layers are exposed. Concretions are internal features of these formations.
- Check for Nuclei. Sometimes, breaking open a concretion (if permitted and safe) can reveal a central nucleus, such as a fossil fragment, shell, or plant material, which initiated its growth.
- Observe Color and Texture Differences. Concretions often have a distinct color and feel (harder, more compact) compared to the surrounding, less cemented sandstone.
Quick Check
- Color:
- Variable (brown, red, yellow, gray), often contrasting with host rock.
- Luster:
- Dull to earthy.
- Streak:
- White, light brown, or reddish-brown, depending on the cementing agent (e.g., calcite, iron oxides).
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