Ferrihydrite | |
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![]() Mine drainage from Ohio. The orange coating on the logs is ferrihydrite. | |
General | |
Category | Oxide minerals |
Formula (repeating unit) | (Fe3+)2O3·0.5H2O |
IMA symbol | Fhy[1] |
Strunz classification | 4.FE.35 |
Dana classification | 04.03.02.02 |
Crystal system | Hexagonal |
Crystal class | Dihexagonal pyramidal (6mm) H-M symbol: (6mm) |
Space group | P63mc |
Unit cell | a = 5.958, c = 8.965 [Å]; Z = 1 |
Identification | |
Formula mass | 168.70 g/mol |
Color | Dark brown, yellow-brown |
Crystal habit | Aggregates, microscopic crystals |
Streak | Yellow-brown |
Diaphaneity | Opaque |
Density | 3.8 g/cm3 |
References | [2][3][4][5] |
Ferrihydrite (Fh) is a widespread hydrous ferric oxyhydroxide mineral at the Earth's surface,[6][7] and a likely constituent in extraterrestrial materials.[8] It forms in several types of environments, from freshwater to marine systems, aquifers to hydrothermal hot springs and scales, soils, and areas affected by mining. It can be precipitated directly from oxygenated iron-rich aqueous solutions, or by bacteria either as a result of a metabolic activity or passive sorption of dissolved iron followed by nucleation reactions.[9] Ferrihydrite also occurs in the core of the ferritin protein from many living organisms, for the purpose of intra-cellular iron storage.[10][11]