Feroxyhyte
Feroxyhyte is a mineral with the chemical formula δ-FeOOH. It is a polymorph of goethite and lepidocrocite, all three having the same chemical composition but differing in crystal structure. Feroxyhyte typically forms as a result of the oxidation of iron(II) compounds in aquatic environments, often under near-neutral to alkaline pH conditions. It is commonly found in hydromorphic soils, lake sediments, and rust scales.
Feroxyhyte is characterized by its poor crystallinity and fine particle size. This makes it difficult to identify using traditional X-ray diffraction techniques, often requiring more advanced methods like transmission electron microscopy. It generally appears as a dark brown or reddish-brown powder or coating.
The structure of feroxyhyte is characterized by double chains of FeO6 octahedra, linked by hydrogen bonds. This distinguishes it structurally from goethite and lepidocrocite, which have different arrangements of the same basic FeOOH building blocks.
The presence of feroxyhyte can influence the geochemical cycling of iron and other elements in the environment. Its reactivity and surface area make it an important sorbent for various contaminants, affecting their mobility and bioavailability. Understanding the formation and stability of feroxyhyte is therefore important in environmental science and geochemistry.