Where is Iron Concretion in Sandstone found?
Iron oxide concretion in sandstone
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Open the appIron Concretion 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 Iron Concretion in Sandstone
Theodore Roosevelt National Park, North Dakota, USA
Famous for abundant 'cannonball' concretions weathered out of the Paleocene Sentinel Butte Formation.
Moeraki Boulders, New Zealand
Large, spherical septarian concretions, primarily calcite-cemented mudstone, but often with iron oxide staining and some ferruginous components.
Katiki Boulders, New Zealand
Similar to Moeraki, these are large concretions found in mudstone, often with iron oxide components.
Utah and Arizona, USA
Common in various Mesozoic sandstone formations, such as the Navajo Sandstone and Entrada Sandstone, often forming 'hoodoos' or 'goblins' where they protect underlying softer rock.
Various locations globally
Iron concretions are a common diagenetic feature in sandstones worldwide, wherever conditions for iron precipitation have occurred.
Collecting tips
- Look for differential weathering. Concretions are typically harder than the surrounding host rock. Look for rounded or irregular masses protruding from weathered outcrops, or lying loose on the ground where the softer host rock has eroded away.
- Examine stream beds and eroded slopes. These areas often expose concretions that have been liberated from their parent rock by erosion.
- Check for color contrast. The reddish-brown to black color of iron concretions often contrasts sharply with the lighter color of the host sandstone.
- Investigate sedimentary rock outcrops. Specifically target sandstone units in road cuts, cliffs, and quarries.
Quick Check
- Color:
- Reddish-brown to dark brown/black
- Luster:
- Dull to earthy
- Streak:
- Reddish-brown to yellowish-brown (for goethite/hematite components)
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