The dark brown material is lepidocrocite, Fe(OH). It is often found with goethite, also FeO(OH) in iron ore deposits. The hydrous iron oxide -FeO(OH) forms when — Photo: Shannon Heinle · CC0
Lepidocrocite
The γ-polymorph of iron oxyhydroxide — an orthorhombic rust-red mineral that gives iron rust its color and streaks quartz with red.
Intro adapted from Wikipedia (CC BY-SA).
Lepidocrocite is an IMA-recognized mineral species in the oxides & hydroxide class, with the chemical formula Fe³⁺O(OH).
It crystallizes in the orthorhombic crystal system (space group Bbmm). It is a member of the Lepidocrocite structural group.
Key properties: Mohs hardness 5; specific gravity 4.09; typically red or orange or brown; Dull orange streak; Submetallic luster; refractive index 2.217; optically biaxial.
IMA symbol Lpc, IMA status: approved, named in 1813.
A weathering or oxidation product of other iron-bearing minerals, in soils and mineral deposits; a precipitate from ground water. In marine manganese nodules.
It is found associated with Goethite, pyrite.
Its name comes from the Greek for scale and thread, for the occasionally feathery or scaly habit.
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