Where is Iron Concretion found?
Iron oxide/hydroxide (e.g., Goethite, Hematite) with Quartz
Got a photo? Identify rocks instantly with the Rockby app
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
Famous for 'Moqui Marbles' (also known as 'Navajo Cherries'), which are spherical iron concretions found in the Navajo Sandstone. These are primarily hematite-cemented sandstone concretions.
Kansas, USA
Known for large, often spherical or discoidal iron concretions found in Cretaceous shales and sandstones, particularly in the Smoky Hill Chalk Member of the Niobrara Formation.
North Dakota, USA
Large, often septarian iron concretions are found in the Cannonball Formation, a Paleocene marine sedimentary unit.
England, UK
Ironstone concretions are common in Jurassic and Cretaceous sedimentary sequences, such as the Lias Group and Wealden Group.
Australia
Extensive occurrences in various sedimentary basins, often associated with lateritic weathering profiles and ancient fluvial systems.
Collecting tips
- Look for Resistant Features. Concretions are typically harder and more resistant to weathering than their host rock. Look for them protruding from outcrops, or as rounded, dense objects in stream beds, fields, or eroded slopes where the softer host rock has been removed.
- Examine Sedimentary Rocks. Focus your search in areas with exposed sedimentary rock formations, especially sandstones, shales, and siltstones. Concretions often form along bedding planes or within specific stratigraphic horizons.
- Check for Iron Staining. The presence of reddish-brown or yellowish-brown staining on rocks and soil in an area can indicate the presence of iron oxides, which are the primary components of iron concretions.
- Break Open Suspect Rocks. Sometimes concretions are partially embedded. Carefully breaking open a suspect rock might reveal the characteristic concentric structure or denser core of a concretion.
- Safety Precautions. When collecting, be aware of your surroundings. Wear appropriate safety gear, including gloves and eye protection, especially if breaking rocks. Always obtain permission before collecting on private land.
Quick Check
- Color:
- Reddish-brown, dark brown, black
- Luster:
- Dull to earthy, sometimes submetallic
- Streak:
- Reddish-brown (hematite-rich) or yellowish-brown (goethite/limonite-rich)
Explore Iron Concretion
Identify rocks anywhere
Free on iOS, Android, and Web. Photo identification, full database, and your personal collection.