sedimentary
Ironstone Concretion (Iron Nodule)
Hydrated Iron Oxide Concretion (predominantly Goethite, Α-FeO(OH), and Hematite, Fe2O3)
AI-generated identification · may be incorrectHardness 5.0–6.0; dark brown to rust-red/black; dull to sub-metallic luster; amorphous to microcrystalline mass; dense specific gravity around 3.5–4.3.
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Physical properties
Hardness 5.0–6.0; dark brown to rust-red/black; dull to sub-metallic luster; amorphous to microcrystalline mass; dense specific gravity around 3.5–4.3.
Formation & geological history
Formed by chemical precipitation of iron-bearing minerals around a central nucleus within sedimentary strata, common from the Paleozoic to Cenozoic eras.
Uses & applications
Primarily collected as geological curiosities; historically smelted on small scales as a minor iron ore source.
Geological facts
Concretions often weather out of softer host rock intact, frequently showing bizarre, brain-like, or fossil-resembling exterior textures.
Field identification & locations
Identifiable by its relatively high density, pitted oxidized crust, and distinctive reddish-brown to yellowish streak on unglazed porcelain.
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