Where is Iron Oxide Concretion found?
Iron Oxide
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Open the appIron Oxide 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 Oxide Concretion
Utah, USA
Famous for 'Moqui Marbles' (also known as 'Navajo Cherries' or 'Shaman Stones'), which are spherical iron oxide concretions found in the Navajo Sandstone formation.
Kansas, USA
Known for large, often septarian, ironstone concretions found in shale and sandstone formations.
England, UK
Ironstone concretions are common in Jurassic and Cretaceous sedimentary sequences, particularly in the Cleveland Ironstone Formation.
Australia
Extensive occurrences of iron oxide concretions and lateritic iron ores are found in weathered profiles across the continent.
Mars
The Mars Exploration Rover Opportunity discovered abundant spherical iron oxide concretions, dubbed 'Martian blueberries,' providing evidence of past water activity.
Collecting tips
- Look in Sedimentary Rocks. Focus your search in areas with exposed sedimentary rock layers, particularly sandstones, shales, and siltstones. Concretions often weather out of softer host rock and can be found loose on the surface.
- Check for Erosion. Riverbeds, stream banks, road cuts, and eroded hillsides are excellent places to find concretions that have been exposed by natural processes.
- Observe Color and Shape. Look for rounded, often spherical or irregular, reddish-brown to black objects that stand out from the surrounding lighter-colored sediment. Their density will also be noticeably higher than typical sedimentary rock.
- Test for Hardness. Iron oxide concretions are generally harder than the surrounding host rock. A steel knife or nail will scratch most sedimentary rocks but may not scratch a well-cemented iron oxide concretion (depending on the specific iron oxide and degree of cementation).
Quick Check
- Color:
- Reddish-brown, dark brown, black, or yellowish-brown.
- Luster:
- Dull to earthy, sometimes submetallic.
- Streak:
- Reddish-brown (for hematite-rich) or yellowish-brown (for goethite/limonite-rich).
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