sedimentary

Ironstone (Limonitic Concretion)

Limonite (FeO(OH)·nH2O) with Goethite and Hematite inclusions

AI-generated identification · may be incorrect

Hardness: 4-5.5 (Mohs scale); Color: Yellowish-brown to dark reddish-brown; Luster: Dull to earthy; Crystal Structure: Amorphous/microcrystalline; Specific Gravity: 2.7-4.3

Hardness: 4-5
Color: Yellowish-brown to dark reddish-brown
Luster: Dull to earthy

Identified February 21, 2026More sedimentary →

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Physical properties

Hardness: 4-5.5 (Mohs scale); Color: Yellowish-brown to dark reddish-brown; Luster: Dull to earthy; Crystal Structure: Amorphous/microcrystalline; Specific Gravity: 2.7-4.3

Formation & geological history

Formed through the chemical precipitation of iron-rich minerals in sedimentary basins or as bog iron, often occurring during the Cenozoic or Mesozoic eras. It commonly forms around a nucleus within sandstone or shale beds.

Uses & applications

Historically used as a low-grade iron ore; currently used as a pigment (ochre), in landscaping, and as decorative stone for rock gardens.

Geological facts

Ironstones often form distinctive 'rattle stones' where a loose core creates sound when shaken. Large deposits in England fueled the early Industrial Revolution's iron production.

Field identification & locations

Identify by its high density relative to other sedimentary rocks and its characteristic rusty streak. Commonly found in deserts (desert varnish) or eroded creek beds. High concentration of iron makes it feel unexpectedly heavy.