Akaganeite

Akaganeite, also written as the deprecated Akaganéite,^[2] is a chloride-containing iron(III) oxide-hydroxide mineral, formed by the weathering of pyrrhotite (Fe_1−xS).

Akaganeite
A piece of the mineral akaganeite. Exhibit of the "Earth and Man" Museum in Sofia, Bulgaria. Discovered in Kaskasnyunchorr, Khibiny Massif, Kola Peninsula, Russia
General
Category	Oxide mineral
Formula	Fe3+O(OH,Cl)
IMA symbol	Akg[1]
Strunz classification	4.DK.05
Crystal system	Monoclinic
Crystal class	Prismatic (2/m) (same H-M symbol)
Space group	I2/m
Unit cell	a = 10.561, b = 3.031 c = 10.483 [Å]; β = 90.63°; Z = 1
Identification
Color	Yellowish brown, rusty brown
Luster	Earthy
Streak	Brownish yellow
Diaphaneity	Transparent, translucent
Specific gravity	3.52

Akaganeite is often described as the β phase of anhydrous ferric oxyhydroxide FeOOH, but some chloride (or fluoride) ions are normally included in the structure,^[3] so a more accurate formula is FeO
_0.833(OH)
_1.167Cl
_0.167.^[4] Nickel may substitute for iron, yielding the more general formula (Fe³⁺
,Ni²⁺
)
₈(OH,O)
₁₆Cl
_1.25^[5]

Akaganeite has a metallic luster and a brownish yellow streak. Its crystal structure is monoclinic 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.^[4]

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,^[6] but named as early as 1961.^[7][8]

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.^[9]

See also

• List of minerals