feroxyhyte

Feroxyhyte is a rare iron oxyhydroxide mineral. It is part of the iron oxide-hydroxide family and is chemically related to goethite (α-FeOOH) and lepidocrocite (γ-FeOOH). The idealized formula is FeOOH, though natural specimens may show substitutions and defects. Feroxyhyte is sometimes described as a high-temperature polymorph or a metastable phase derived from FeOOH, and it has been identified in environments where iron-bearing minerals oxidize under varying temperatures and pH.

Occurrence and formation: Feroxyhyte forms during oxidative alteration of iron minerals in soils, laterites, and hydrothermal or supergene environments. It is typically found as coatings or microscopic crystals in iron-rich rocks and is often associated with goethite, hematite, lepidocrocite, and magnetite.

Properties: Feroxyhyte is typically brown to yellow-brown in color, with an earthy to dull luster. It is relatively soft and forms in fine-grained, weathering-related aggregates. Because of its similarity to other FeOOH minerals, X-ray diffraction and Mössbauer spectroscopy are used to distinguish it from goethite and lepidocrocite.

Importance: As an indicator of redox conditions, the presence of feroxyhyte can signal phases of iron oxidation in geological and environmental records. It is mainly of interest to mineralogists and geologists studying weathering processes and ore genesis.