Red-brown granules of the rare mineral ferrihydrite in a capsule. From: Lake Murtojärvi, Joensuu, North Karelia, Finland. Ex Vandenbroucke Museum collection specimen, from Waregem, Belgium. — Photo: David Hospital · CC BY-SA 4.0
Ferrihydrite
A widespread poorly-crystalline iron oxyhydroxide — the rust-colored precipitate of springs, soils, streams and mine drainage.
Intro adapted from Wikipedia (CC BY-SA).
Ferrihydrite is an IMA-recognized mineral species in the oxides & hydroxide class, with the chemical formula Fe³⁺₁₀O₁₄(OH)₂.
It crystallizes in the hexagonal crystal system (space group P3). It is a member of the Nolanite structural group.
IMA symbol Fhy, IMA status: approved, named in 1971.
Widespread in the soluble fraction of soils and weathered rock. In precipitates around cold and hot springs, especially those supporting iron-metabolizing bacteria; in acid mine effluent.
It is found associated with Goethite, lepidocrocite, hematite, manganese oxides.
The name refers to FERRIc iron in its composition, and a HYDRated mineral.