Where is Iron Concretion found?
Goethite/Limonite (Iron Oxide/Hydroxide)
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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
Midwestern United States
Common in glacial till and sedimentary bedrock, particularly in states like Ohio, Indiana, and Illinois, often found in stream beds and eroded outcrops.
Southeastern United States
Abundant in coastal plain sediments and residual soils derived from iron-rich parent materials, such as in Georgia and Alabama.
Western Australia
Extensive deposits of iron ore, including goethite-rich laterites and pisolitic iron formations, are found in regions like the Pilbara.
Brazil
Significant iron ore deposits, including goethite and limonite, are found in lateritic soils and banded iron formations, particularly in Minas Gerais.
Europe (e.g., Germany, France, UK)
Historically important bog iron deposits and ironstone concretions are found in various sedimentary basins and wetland areas.
Collecting tips
- Look in Sedimentary Outcrops. Examine exposed sedimentary rock layers, especially sandstones and shales, for rounded or irregular masses that stand out due to their hardness and color.
- Check Stream Beds and Riverbanks. Water erosion often exposes and concentrates concretions in stream beds, gravel bars, and along riverbanks.
- Explore Weathered Soils and Road Cuts. In areas with iron-rich soils or underlying sedimentary rocks, concretions can be found in weathered horizons, road cuts, and construction sites.
- Use a Magnet (with caution). While goethite/limonite are not strongly magnetic, some concretions may contain minor amounts of magnetite or maghemite, or be associated with other magnetic minerals. A weak attraction might be observed, but it's not a definitive test.
- Observe Color and Density. Their characteristic reddish-brown to yellowish-brown color and relatively high density (they feel heavy for their size) are good indicators.
Quick Check
- Color:
- Yellowish-brown to dark brown
- Luster:
- Dull, earthy, or submetallic
- Streak:
- Yellowish-brown to brownish-yellow
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