mineral

Limonite Concretion

Hydrated iron oxide-hydroxide, FeO(OH)·nH2O

Hardness of 4-5.5 on the Mohs scale, yellowish-brown to dark brown color, earthy to sub-metallic luster, amorphous crystal structure.

Identified October 23, 2026More mineral →

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Physical properties

Hardness of 4-5.5 on the Mohs scale, yellowish-brown to dark brown color, earthy to sub-metallic luster, amorphous crystal structure.

Forms through the oxidation of iron-rich minerals and precipitation in weathering zones or sedimentary environments.

Historically used as a yellow-brown pigment (ochre) and as a minor ore of iron.

Also known as brown iron ore, limonite often forms in nodular masses or crusts and was used by ancient humans for cave paintings.

Identify by its characteristic yellowish-brown streak and irregular concretionary form; found worldwide in weathered iron deposits.

Gneiss or Schist

Gneiss or Mica Schist with Garnet

Limonite

FeO(OH)•nH2O

Sandstone (with potential mineral staining/concretions)

Arenite (SiO2 based)

Feldspar

Feldspar Group (Tectosilicate, e.g., KAlSi3O8)

Tumbled granite

Granite, a coarse-grained felsic intrusive igneous rock

Pegmatite with Tourmaline and Quartz

Igneous Pegmatite