akaganéites

Akaganéites are a group of naturally occurring iron oxyhydroxide minerals. The most common form is akaganéite, with the chemical formula Fe8O8(OH)6Cl. Other related minerals in this group include feoxenite and limonite, though these terms are often used more broadly. Akaganéites typically form in environments where iron-rich solutions interact with chloride ions, often under alkaline conditions. They are frequently found in oxidizing zones of hydrothermal veins and as alteration products of iron-bearing minerals in various geological settings.

These minerals are characterized by their yellowish-brown to reddish-brown color and a fibrous or needle-like crystal structure. They are generally soft and have a low specific gravity. Akaganéites are not typically economically significant, but they can be important indicators of specific geological processes and the presence of oxidizing, chloride-rich waters. They are sometimes encountered in archaeological contexts as a result of iron object corrosion. The name "akaganéite" is derived from the Akagané mine in Japan, where it was first described. While akaganéite itself is a specific mineral, the broader term "akaganéites" can encompass a range of related iron oxyhydroxides with varying compositions, often including other anions besides chloride.