Iron hydroxides (Limonite/Goethite)
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Mineral NameIron hydroxides (Limonite/Goethite)
Chemical FormulaFeO(OH)·nH₂O
Mohs Hardness5
Streak Coloryellowish-brown
Cleavagenone (in cryptocrystalline aggregates)
Fractureuneven/conchoidal
Specific Gravity3.3
Colorsyellow, orange, brown, dark brown
Transparencytranslucent/opaque
Type LocalityNot specified
Mineral GroupOxides/Hydroxides
Usesminor iron ore, pigment, collector specimens
Associated Mineralsplagioclase, pyroxene, olivine, volcanic glass (within basalt)
Raritycommon
Description
A concentrically banded, kidney-shaped aggregate of iron hydroxides, displaying shades of yellow, orange, and brown, filling a void (vesicle) within a fine-grained, dark igneous rock (basalt).
Geological Context
These iron hydroxides formed as secondary minerals, likely from the alteration of iron-bearing minerals in the basalt or from hydrothermal fluids, precipitating in layers within a pre-existing gas vesicle in the volcanic rock.
