Akaganeite, also written as the deprecated Akaganéite,Ernst A.J. Burke (2008). "Tidying up Mineral Names: an IMA-CNMNC Scheme for Suffixes, Hyphens and Diacritical marks". Mineralogical Record. 39 (2). is a chloride-containing iron(III) oxide-hydroxide mineral, formed by the weathering of pyrrhotite (Fe1−xS), an iron-deficient sulfide.
Akaganeite is often described as the β phase of anhydrous ferric oxyhydroxide , but some chloride (or fluoride) anions are commonly included in the structure,Jongsik Kim and Clare P. Grey (2010). "Li Solid-State MAS-NMR Study of Local Environments and Lithium Adsorption on the Iron(III) Oxyhydroxide, Akaganeite (β-FeOOH)". Chemistry of Materials. 22, 5453–5462. so a more accurate formula is .C. Rémazeilles and Ph. Refait (2007). "On the formation of β-FeOOH (akaganéite) in chloride-containing environments". Corrosion Science, 49 (2), 844–857. This formula derives from the more general expression , where x = 1/6 ≃ 0.167. As the anion is doubly negatively charged, to maintain the electroneutrality in the crystal lattice, the electrical charge deficit (2x) in must be compensated by two monovalent anions, one and one . Nickel may substitute for iron, yielding the more general formula "Mineral 314–687: Akaganeite". Mindat.org database, accessed on 2019-02-12.
Akaganeite has a metallic luster and a brownish yellow streak. Its crystal structure is monoclinic and similar to that of hollandite , characterised by the presence of tunnels parallel to the c-axis of the tetragonal lattice. These tunnels are partially occupied by chloride anions, which provide the crystal with its structural stability.
Occurrence 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,Matsuo Nambu (1968). "岩手県赤金鉱山産新鉱物赤金鉱 (β-FeOOH) について (New mineral Akaganeite, β-FeOOH, from Akagane Mine, Iwate Prefecture, Japan)", Journal of the Japanese Association of Mineralogists, Petrologists and Economic Geologists, volume 59, issue 4, pages 143-151, but named as early as 1961.Alan Lindsay Mackay (1962). "β-ferric oxyhydroxide – akaganéite". Mineralogical Magazine and Journal of the Mineralogical Society. 33 (259), 270–280. Cites a private communication by Matsuo Nambu (1961). Note: the diacritic in the title is incorrect, see Burke (2008). Reviewed by Mandarino (1963) in American MineralogistJ. A. Mandarino (1963). "New Mineral Names: Akaganéite". American Mineralogist. 48 (5-6), 711. Short review of Mackay's communication (1962) in Mineralogical Magazine. Note: the diacritic in the title is incorrect.
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.
See also Feroxyhyte Ferrihydrite Iron(III) oxide-hydroxide Lepidocrocite List of minerals
References
External links Mindat with locations Webmineral Weisstein