Akaganeite, also written as the deprecated Akaganéite, -containing iron(III) oxide-hydroxide , formed by the weathering of pyrrhotite (Fe1−xS).
Akaganeite is often described as the β phase of anhydrous ferric oxyhydroxide (or fluoride so a more accurate formula is FeO 0.833(OH) 1.167Cl 0.167. may substitute for iron, yielding the more general formula (Fe3+,Ni2+ ) 8(OH,O) 16Cl 1.25
Akaganeite has a metallic and a brownish yellow streak. Its crystal structure and similar to that of hollandite BaMn 8O 16, characterised by the presence of tunnels parallel to the c-axis of the tetragonal lattice. These tunnels are partially occupied by chloride anions that give to the crystal its structural stability.