Where is Concretion found?
Sedimentary Concretion
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Open the appConcretion 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
Mazon Creek, Illinois, USA
Famous for exceptionally well-preserved plant and animal fossils within siderite (iron carbonate) concretions in Pennsylvanian-age shales.
Moeraki Boulders, New Zealand
Large, spherical septarian concretions eroded from Paleocene mudstone.
Cannonball River, North Dakota, USA
Known for large, spherical sandstone concretions resembling cannonballs.
Kimberley Region, Western Australia
Contains 'gogotte' concretions, which are intricate, sand-cemented forms.
Various sedimentary basins worldwide
Concretions are ubiquitous in sedimentary rock sequences globally, particularly in fine-grained clastic rocks and limestones.
Collecting tips
- Look for spherical or ovoid shapes. Concretions often stand out from the surrounding host rock due to their distinct, often rounded, morphology.
- Check weathered outcrops. Concretions are typically harder and more resistant to weathering than the surrounding sediment, causing them to protrude from weathered rock faces or accumulate as lag deposits.
- Examine stream beds and beaches. Erosion can liberate concretions from their host rock, transporting them to stream beds, river banks, or coastal areas.
- Investigate sedimentary layers. Concretions form within specific sedimentary beds; understanding the local stratigraphy can help pinpoint their occurrence.
- Look for color and compositional differences. The color and composition of a concretion often differ from the surrounding matrix, making them visually distinct.
Quick Check
- Color:
- Variable (gray, brown, black, red, yellow, white)
- Luster:
- Dull to earthy
- Streak:
- Variable, often white, brown, or reddish-brown, depending on composition.
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