Where is Iron Concretion found?
Goethite/Hematite concretion
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Open the appIron 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 Iron Concretion
Utah, USA
The Navajo Sandstone in southern Utah is famous for its 'Moqui Marbles,' which are iron concretions primarily composed of hematite, often spherical and ranging from pea-sized to several centimeters.
North Dakota, USA
The Cannonball River area is known for large, spherical iron concretions, sometimes several meters in diameter, found in the Paleocene Cannonball Formation.
England, UK
The Jurassic shales and sandstones of the Yorkshire coast and other areas contain numerous ironstone concretions, often preserving fossils.
Canada
Various sedimentary basins across Canada, particularly in Cretaceous and Tertiary formations, host iron concretions.
Mars
The Mars Exploration Rover Opportunity discovered abundant small, spherical hematite concretions, dubbed 'Martian blueberries,' in Meridiani Planum, indicating past water activity.
Collecting tips
- Look in Sedimentary Rocks. Focus your search in areas with exposed sedimentary rock formations, particularly sandstones, siltstones, and shales. Concretions are often more resistant to weathering than the host rock and may stand out.
- Check Eroded Surfaces. Concretions are frequently found loose on the ground in areas where the surrounding softer rock has eroded away, leaving the harder concretions behind as lag deposits.
- Examine Stream Beds and Beaches. Water erosion can concentrate concretions in stream beds, river banks, and coastal areas where they have been washed out of their original rock matrix.
- Look for Distinct Shapes. Keep an eye out for spherical, ovoid, or unusually shaped rocks that are denser and often darker than the surrounding material. Some may have a 'rattle' if they are hollow inside.
- Observe Color and Streak. The characteristic reddish-brown to black color and a reddish-brown or yellowish-brown streak (when scratched on an unglazed porcelain plate) are good indicators of iron oxides.
Quick Check
- Color:
- Reddish-brown, dark brown, yellowish-brown, black
- Luster:
- Dull to earthy, sometimes submetallic
- Streak:
- Reddish-brown (hematite-rich) or yellowish-brown (goethite-rich)
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