What is Lepidocrocite?
Lepidocrocite is a red to reddish-brown iron oxyhydroxide that forms in weathering environments and gives iron-rich coatings their vivid colour.
Mineralogy and crystal structure
Reference formula: FeO(OH). Lepidocrocite is an orthorhombic polymorph of FeO(OH), related to goethite. Its platy crystal habit and red colour often occur at fine grain size or in intergrowths, so powder X-ray diffraction or microscopy may be needed for confident identification. Lepidocrocite is classified with oxides and has a orthorhombic crystal system. Typical hardness is 4–5 on the Mohs scale and specific gravity is approximately 4.0–4.1.
Colour, lustre and habit
Typical colours include red, reddish-brown, orange, brown. The usual scaly, platy, fibrous habit and sub-metallic, vitreous, dull lustre help describe a specimen, but colour alone is not diagnostic.
Formation and notable localities
Lepidocrocite forms in or is associated with oxidation of iron-bearing minerals in soils, bog iron, mine environments and sedimentary deposits. Important documented localities include Germany, France, the United Kingdom, the United States, Brazil and Australia.
A vivid iron-red surface mineral
Lepidocrocite turns ordinary weathering into a strong visual feature. Its scarlet to rust-red films and scales make a compelling accent specimen, while the close relationship with goethite gives collectors a concise lesson in iron-oxide mineralogy.
Collecting and care
Avoid abrasive cleaning and dust; keep the specimen dry and do not assume a red iron coating is lepidocrocite without analysis.
