sedimentary
Ironstone Concretion
Ferruginous Siltstone/Ironstone (Fe2O3)
Hardness: 5-6 (variable); Color: reddish-brown, tan, or deep rust; Luster: dull, earthy; Crystal structure: massive/amorphous; Cleavage: none; Specific Gravity: 3.5-5.0
- Hardness
- 5-6 (variable)
- Color
- reddish-brown, tan, or deep rust
- Luster
- dull, earthy
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Physical properties
Hardness: 5-6 (variable); Color: reddish-brown, tan, or deep rust; Luster: dull, earthy; Crystal structure: massive/amorphous; Cleavage: none; Specific Gravity: 3.5-5.0
Formation & geological history
Formed by the precipitation of mineral cement, typically iron oxides, within the spaces between sediment grains (sand or silt) in sedimentary basins, often over millions of years.
Uses & applications
Primarily used as an iron ore in some regions; also used for landscaping pebbles or decorative specimens.
Geological facts
Concretions are often mistaken for meteorites or dinosaur eggs due to their unusual shapes and heavy weight. They can sometimes contain fossils at their core.
Field identification & locations
Identify by its high density compared to surrounding rocks, distinct rusty orange/brown weathering rind, and its resistance to erosion. Found in sedimentary environments worldwide.
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