mineral
Limonite or Ironstone Concretion
FeO(OH)·nH₂O (Hydrated iron oxide-hydroxide)
Hardness varies from 4 to 5.5 on the Mohs scale, color ranges from yellowish-brown to dark brown and black, luster is earthy to submetallic, and it has no distinct crystal system as it is typically amorphous or microcrystalline.
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Physical properties
Hardness varies from 4 to 5.5 on the Mohs scale, color ranges from yellowish-brown to dark brown and black, luster is earthy to submetallic, and it has no distinct crystal system as it is typically amorphous or microcrystalline.
Formation & geological history
Formed through the oxidation and weathering of iron-rich sulfide minerals or as chemical precipitates in sedimentary environments, often found in bog ores, gossans, and soil iron crusts.
Uses & applications
Historically used as a pigment (ochre), a low-grade ore for iron production, and as a specimen for mineral collectors.
Geological facts
Limonite is not a true standalone mineral species, but rather a mixture of related hydrated iron oxides, most commonly goethite and lepidocrocite.
Field identification & locations
Can be identified by its characteristic yellowish-brown to brownish-black streak, high density/weight relative to its size, and common association with iron staining in surrounding rocks.
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Arenite (SiO2 based)
sedimentary
Soil with Mineral Detritus and Quartz Fragments
Regolith / Silicate Mineral Aggregate
sedimentary
Limonite / Goethite (Iron Ore Mineral nodule)
FeO(OH)·nH2O / FeO(OH)
mineral
Septarian Pebble
Septarian nodule / Concretion
sedimentary
Schist
Schist
Metamorphic
Potassium Feldspar (Orthoclase)
Orthoclase (KAlSi3O8)
mineral