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A piece of the mineral akaganéite. Exhibit of the "Earth and Man" Museum in Sofia, Bulgaria. Discovered in Kaskasnyunchorr, Khibiny Massif, Kola Peninsula, Russia
Category Oxide mineral
(repeating unit)
Strunz classification 04.DK.05
Crystal symmetry 2/m - Prismatic
Unit cell

a = 10.561Å, b = 3.031Å, c = 10.483Å

β = 90.63°
Color Yellowish brown, rusty brown
Crystal system Monoclinic
Luster Earthy
Streak Brownish yellow
Diaphaneity Transparent, translucent
Specific gravity 3.52

Akaganéite is an iron(III) oxide-hydroxide / chloride mineral with formula: Fe3+O(OH,Cl) e.g.; β-FeO(OH). It is formed by the weathering of pyrrhotite (Fe1-xS). Nickel also has been reported in the structure. It has a monoclinic crystal structure, a metallic luster and a brownish yellow streak. It is named after the Akagane mine in Iwate, Japan, in which it was discovered. It 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.