Where is Sandstone Concretion found?
Sedimentary rock, likely composed of quartz grains cemented by iron oxides or carbonates
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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
Famous for its 'cannonball concretions' in the badlands, formed in the Paleocene Sentinel Butte Formation.
Moeraki Boulders, Otago, New Zealand
Large, spherical septarian concretions found on Koekohe Beach, formed in Paleocene mudstone.
Bowling Ball Beach, Mendocino County, California, USA
Features rows of spherical concretions exposed at low tide, formed in Miocene mudstone.
Bisti/De-Na-Zin Wilderness, New Mexico, USA
Contains numerous bizarrely shaped sandstone concretions and hoodoos in the Cretaceous Kirtland Shale and Fruitland Formation.
Kata Tjuta (The Olgas), Northern Territory, Australia
While not individual concretions, the conglomerate rock forming Kata Tjuta contains large, rounded clasts cemented together, representing a form of localized cementation on a larger scale, and concretions can be found in associated sedimentary units.
Collecting tips
- Look for Differential Weathering. Concretions are typically harder than the surrounding host rock. Look for areas where softer sedimentary layers have eroded away, leaving the more resistant concretions exposed on the surface, often as rounded or irregular lumps.
- Examine Eroded Outcrops and Stream Beds. Riverbeds, coastal cliffs, badlands, and road cuts are excellent places to find concretions, as these environments expose fresh rock and allow for the removal of softer material.
- Check for Nuclei. Sometimes, breaking open a concretion (if permitted and safe) can reveal a central nucleus, such as a fossil fragment, around which the concretion grew. This can be a good indicator of its origin.
- Observe Shape and Size. Concretions come in various shapes (spherical, ovoid, discoidal, irregular) and sizes. Spherical 'cannonball' concretions are particularly distinctive.
- Distinguish from Boulders. Ensure the object is not a transported boulder or cobble. Concretions are typically formed in situ within the sedimentary layer, and their composition should match the surrounding host rock's sand grains, albeit with a different cement.
Quick Check
- Color:
- Variable (reddish-brown, yellow, gray, white) depending on cement.
- Luster:
- Dull to earthy.
- Streak:
- White, or the color of the cementing agent if it is abundant (e.g., reddish-brown for hematite).
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