lepidocrociteand

Lepidocrocite is an iron oxyhydroxide mineral with the approximate formula FeO(OH)·nH2O, commonly described as gamma-FeO(OH). It forms as a hydrated iron oxide in near-surface environments and is a common corrosion product of iron and steel in moist conditions. Lepidocrocite typically occurs as reddish-brown to yellowish-brown, flaky platelets or scales and can be found in soils, sediments, and ultramafic or hydrothermal settings where oxidation of ferrous iron takes place.

Crystal structure and appearance: Lepidocrocite crystallizes in an orthorhombic system and is characterized by its fine, lamellar habit. The material consists of iron(III) centers coordinated by oxide and hydroxide groups, with water molecules weakly bound in the structure. Its physical appearance ranges from earthy to platy crystals, often forming as delicate plates that contribute to the rust-colored coloration in rocks and artifacts.

Formation and transformation: It forms during the oxidation of Fe2+ in near-surface environments, including weathering of iron minerals, steel corrosion, and iron-rich sediments. Lepidocrocite is metastable relative to goethite (alpha-FeO(OH)); upon dehydration or aging, it can transform toward goethite. Over longer times and varying conditions, goethite and hematite can become more prominent as the system equilibrates.

Occurrence, associations, and significance: It is commonly associated with other iron oxyhydroxides and oxides such as goethite, ferrihydrite, and hematite. In archaeology and materials science, the presence of lepodocrocite can indicate specific corrosion or diagenetic histories, including moisture and chloride-rich environments. Analytical techniques such as X-ray diffraction and electron microscopy are used to identify its characteristic lamellar crystals and to distinguish it from related minerals.

Etymology and naming: The name reflects its scale-like or plate-like crystal habit observed in many samples.