mineral
Limonite or Ironstone Concretion
FeO(OH)·nH₂O (Hydrated iron oxide-hydroxide)
AI-generated identification · may be incorrectHardness 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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Gneiss or Schist
Gneiss or Mica Schist with Garnet
Metamorphic
Sandstone (with potential mineral staining/concretions)
Arenite (SiO2 based)
sedimentary
Epidote
Epidote | Ca2(Al2,Fe3+)(SiO4)(Si2O7)O(OH)
metamorphic
Pegmatite with Tourmaline and Quartz
Igneous Pegmatite
igneous
Granite
Granite (Phaneritic intrusive igneous rock)
igneous
Septarian Pebble
Septarian nodule / Concretion
sedimentary