gammaFeOOH

Gamma-FeOOH refers to a ferric oxyhydroxide phase known as lepidocrocite. It is the gamma polymorph of iron oxyhydroxide (FeO(OH)) and is commonly described as hydrated ferric oxyhydroxide. Like other FeOOH minerals, it forms under oxidizing conditions, but it is metastable compared with other phases such as goethite and hematite.

The structure of gamma-FeOOH consists of FeO6 octahedra connected to form sheets, with hydroxide ions and interlayer water molecules linking the sheets. This layered arrangement gives lepidocrocite a relatively high surface area and distinct physical properties compared with its alpha counterpart, goethite.

In nature, lepidocrocite appears as a component of iron-rich soils, sediments, and rust layers, and is frequently produced during the oxidation of Fe2+ in aqueous environments. It can also form as a corrosion product on steel in the presence of water and oxygen, especially under conditions that favor kinetically controlled growth.

Lepidocrocite is typically considered a transient or metastable phase that can transform to goethite or hematite over time, particularly with aging, dehydration, or heating. These transformations influence the magnetic, optical, and adsorption properties of the material.

Properties of gamma-FeOOH include a reddish-brown to yellow-brown color, paramagnetism at ambient temperature, and a high surface area that promotes adsorption of various ions and molecules. Because of its reactive surface, gamma-FeOOH has been studied as a precursor phase in mineral transformations and as a component in environmental remediation and catalysis research.