sedimentary

Ironstone (Limonite/Hematite concretion)

Ferruginous Siltstone / Goethite (FeO(OH))

AI-generated identification · may be incorrect

Hardness: 4.0-5.5 Mohs; Color: dark brown to rusty orange-brown; Luster: earthy to sub-metallic; Crystal Structure: Amorphous or Cryptocrystalline; Specific Gravity: 3.3-4.3

Hardness: 4
Color: dark brown to rusty orange-brown
Luster: earthy to sub-metallic

Identified July 1, 2026More sedimentary →

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Physical properties

Hardness: 4.0-5.5 Mohs; Color: dark brown to rusty orange-brown; Luster: earthy to sub-metallic; Crystal Structure: Amorphous or Cryptocrystalline; Specific Gravity: 3.3-4.3

Formation & geological history

Formed by the precipitation of iron oxides from groundwater, often concentrating around a nucleus in sedimentary layers. These typically form in oxygen-rich environments where iron moves in solution and deposits as cement between mineral grains.

Uses & applications

Historically used as a low-grade iron ore; commonly used today in landscaping, as a decorative mineral specimen, or as a natural pigment (ochre).

Geological facts

Ironstone concretions are frequently mistaken for meteorites because of their high density and dark, weathered rinds, earning them the nickname 'meteor-wrongs'. Some ironstones contain hollow centers or fossil imprints.

Field identification & locations

Identify in the field by its high density relative to other sedimentary rocks and its characteristic rusty streak test (giving a yellow or reddish-brown streak on unglazed porcelain). Found globally in sedimentary basins.