Ferrihydrite
Chemical compound
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Ferrihydrite is a widespread hydrous ferric oxyhydroxide mineral at the Earth's surface, and a likely constituent in extraterrestrial materials. It forms in several types of environments, from freshwater to marine systems, aquifers to hydrothermal... Wikipedia
Formula mass: 168.70 g/mol
Density: 3.8 g/cm3
Color: Dark brown, yellow-brown
Crystal class: Dihexagonal pyramidal (6mm); H-M symbol: (6mm)
Crystal habit: Aggregates, microscopic crystals
Crystal system: Hexagonal
Formula (repeating unit): (Fe3+)2O3·0.5H2O