sedimentary
Ironstone Concretion
Siderite or Goethite Concretion
Hardness: 4-5.5 Mohs; Color: Rusty brown, reddish-orange to dark blackish-brown; Luster: Dull to earthy; Crystal Structure: Amorphous or microcrystalline; Cleavage: None; Density: Heavy due to iron content.
- Hardness
- 4-5
- Color
- Rusty brown, reddish-orange to dark blackish-brown
- Luster
- Dull to earthy
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Physical properties
Hardness: 4-5.5 Mohs; Color: Rusty brown, reddish-orange to dark blackish-brown; Luster: Dull to earthy; Crystal Structure: Amorphous or microcrystalline; Cleavage: None; Density: Heavy due to iron content.
Formation & geological history
Formed by the precipitation of iron minerals (like siderite, goethite, or limonite) from groundwater within the pore spaces of sedimentary rocks. This specimen appears to have formed around or adhered to an organic shell fragment.
Uses & applications
Largely used as a source of iron ore historically; currently of interest to geology collectors, for educational study, and sometimes used as decorative accents in landscaping.
Geological facts
Concretions are often mistaken for fossils or meteorites due to their unusual shapes. They grow outward from a central nucleus, which can be a leaf, shell, or bone.
Field identification & locations
Identified by its high density/weight relative to size, rusty coloration, and often rounded or irregular lumpy shapes. Commonly found in riverbeds, eroding cliffs, and sandstone deposits.
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