sedimentary

Ironstone Concretion (Limonite/Hematite Nodules)

Ironstone (principally Limonite FeO(OH)·nH2O or Hematite Fe2O3 mixed with silica/clay)

AI-generated identification · may be incorrect

Hardness: 4.0-5.5 (Mohs scale); Color: Rusty brown, reddish-orange, or dark ochre; Luster: Dull, earthy; Crystal structure: Amorphous or microcrystalline; Cleavage: None; Specific Gravity: 2.7–4.3 depending on iron concentration.

Hardness: 4
Color: Rusty brown, reddish-orange, or dark ochre
Luster: Dull, earthy

Identified March 18, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed by the precipitation of iron-rich minerals in the spaces between sediment grains (usually sandstone or shale). These often form around a nucleus of organic material or a different mineral within sedimentary basins. They can range from millions to several hundred million years old.

Uses & applications

Historically used as a low-grade iron ore. Mostly used today for decorative landscaping, small carvings, or as educational geological specimens (popularly known as 'Moqui Marbles' or 'Shaman Stones' in specific regions).

Geological facts

They are often mistaken for meteorites due to their heavy weight and dark, weathered crust. Some concretions contain hollow centers or 'rattlestones' where the interior material has dried and detached from the outer shell.

Field identification & locations

Identify by the heavy weight for its size, rusty streak when rubbed on unglazed porcelain, and distinctive rounded or potato-like shape. Commonly found in eroded sandstone landscapes, stream beds, and desert environments worldwide.