sedimentary

Ironstone Concretion (Pot Stone)

Siderite or Limonite Concretion (FeCO3 or FeO(OH)·nH2O)

AI-generated identification · may be incorrect

Hardness: 4.0-5.5 on Mohs scale; Color: Rusty brown, ochre, or reddish-tan; Luster: Dull/Earthy; Crystal Structure: Cryptocrystalline; Cleavage: None/Irregular; Specific Gravity: 3.0-3.9

Hardness: 4
Color: Rusty brown, ochre, or reddish-tan
Luster: Dull/Earthy

Identified March 26, 2026More sedimentary →

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Physical properties

Hardness: 4.0-5.5 on Mohs scale; Color: Rusty brown, ochre, or reddish-tan; Luster: Dull/Earthy; Crystal Structure: Cryptocrystalline; Cleavage: None/Irregular; Specific Gravity: 3.0-3.9

Formation & geological history

Formed by the precipitation of mineral cement (iron oxides or carbonates) within the spaces between sediment grains, often around a nucleus like a shell or leaf. Typical of the Cretaceous or Carboniferous periods in swampy or marine environments.

Uses & applications

Primarily for geological study, education, or as garden ornaments and curiosities. Historically, some iron-rich concretions were used as low-grade iron ore.

Geological facts

These are often mistaken for man-made bowls, fossilized dinosaur eggs, or ancient artifacts due to their symmetrical 'pot' shape. They are actually entirely natural geological formations.

Field identification & locations

Identify in the field by their rounded, bowl-like or spherical shapes and heavy weight relative to size. Commonly found in eroded sandstone or clay beds in the UK, USA (Ohio, Kansas), and Australia.