Akaganeite, also written as the deprecated Akaganeite, is a chloride-containing iron(III) oxide-hydroxide mineral, formed by the weathering of pyrrhotite (Fe1−xS).

Akaganeite is often described as the b phase of anhydrous ferric oxyhydroxide FeOOH, but some chloride (or fluoride) ions are normally included in the structure, so a more accurate formula is FeO0.833(OH)1.167Cl0.167.
Nickel may substitute for iron, yielding the more general formula (Fe3+,Ni2+)8(OH,O)16Cl1.25

Akaganeite has a metallic luster and a brownish yellow streak. Its crystal structure is monoclinic and similar to that of hollandite BaMn8O16, 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.

The mineral was discovered in the Akagane mine in Iwate, Japan, for which it is named. It was described by the Japanese mineralogist Matsuo Nambu in 1968, but named as early as 1961.

Akaganeite has also been found in widely dispersed locations around the world and in rocks from the Moon that were brought back during the Apollo Project. The occurrences in meteorites and the lunar sample are thought to have been produced by interaction with Earth’s atmosphere. It has been detected on Mars through orbital imaging spectroscopy.

List of minerals

This article about a specific oxide mineral is a stub. You can help Wikipedia by expanding it.