mineral
Limonite / Iron Oxide Concretion
FeO(OH)·nH2O (Hydrated iron(III) oxide-hydroxide)
AI-generated identification · may be incorrectHardness 4–5.5 Mohs, earthy yellow-brown to dark brown color, dull or earthy luster, amorphous to cryptocrystalline, irregular to subconchoidal fracture.
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Physical properties
Hardness 4–5.5 Mohs, earthy yellow-brown to dark brown color, dull or earthy luster, amorphous to cryptocrystalline, irregular to subconchoidal fracture.
Formation & geological history
Forms secondary to the oxidation and weathering of primary iron-bearing minerals like pyrite, siderite, or magnetite in near-surface sedimentary and soil environments.
Uses & applications
Historically mined as a minor iron ore and used widely as a natural ochre pigment for paints and dyes; minimal modern commercial use.
Geological facts
Commonly forms pseudomorphs after other minerals like pyrite, preserving crystal shapes while altering composition completely.
Field identification & locations
Identified in the field by its distinctive yellowish-brown streak, rough earthy texture, and lack of magnetism compared to magnetite.
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Gneiss or Schist
Gneiss or Mica Schist with Garnet
Metamorphic
Sandstone (with potential mineral staining/concretions)
Arenite (SiO2 based)
sedimentary
Tumbled granite
Granite, a coarse-grained felsic intrusive igneous rock
igneous
Pegmatite with Tourmaline and Quartz
Igneous Pegmatite
igneous
Epidote
Epidote | Ca2(Al2,Fe3+)(SiO4)(Si2O7)O(OH)
metamorphic
Granite
Granite (Phaneritic intrusive igneous rock)
igneous