Where is Iron Oxide Concretion found?
Goethite/Hematite (Fe2O3 H2O / Fe2O3)
Got a photo? Identify rocks instantly with the Rockby app
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
The Navajo Sandstone in southern Utah is famous for 'Moqui Marbles,' which are spherical iron oxide concretions, primarily hematite, often with a sandstone core. These are excellent examples of well-formed concretions.
North Dakota, USA
The Cannonball Concretions of the Cannonball River area are large, spherical iron oxide concretions found in the Paleocene Cannonball Formation, often eroding out of riverbanks.
Kansas, USA
Various shales and sandstones across Kansas contain ironstone concretions, often weathering out of stream beds and road cuts.
England, UK
The Jurassic ironstones of the Cleveland Basin and other areas contain numerous iron oxide concretions, often associated with fossiliferous horizons.
Germany
Bog iron deposits, which are a form of iron oxide concretion, have been historically mined in various regions of Germany.
Collecting tips
- Look in Sedimentary Rocks. Focus your search on areas with exposed sedimentary rock formations, particularly sandstones, siltstones, and shales. Concretions are often harder than the surrounding rock and may weather out, accumulating at the base of outcrops or in stream beds.
- Check for Erosion. Riverbanks, road cuts, and areas undergoing active erosion are excellent places to find concretions that have been liberated from their host rock.
- Observe Color and Shape. Look for dark reddish-brown to black, often spherical, ovoid, or irregularly shaped masses that stand out from the lighter-colored host rock.
- Test Density. Iron oxide concretions are typically denser than common sedimentary rocks. If you pick up a rock that feels unusually heavy for its size, it might be an iron concretion.
- Use a Streak Plate. A reddish-brown to red streak is a strong indicator of iron oxides (goethite/hematite). This can help differentiate them from other dark concretions like manganese nodules (black streak) or chert (no streak).
Quick Check
- Color:
- Dark reddish-brown to black, sometimes yellowish-brown.
- Luster:
- Dull to earthy, occasionally submetallic.
- Streak:
- Reddish-brown to red (for hematite-rich) or yellowish-brown (for goethite-rich).
Explore Iron Oxide Concretion
Identify rocks anywhere
Free on iOS, Android, and Web. Photo identification, full database, and your personal collection.