Constituent
Name
ferrihydrite
Class
non-silicate mineral
Compound type
oxide-hydroxide
Relevance
main - major
Arrangement
unknown
Formula
$Fe^{3+}_2O_3 \bullet 0.5(H_2O)$
Chemical formula
(Fe3+)2O3•0.5(H2O)
Elemental formula
(Fe3+)2 O3.5 H
Isotope mixture type
terrestrial abundance
  Formula Name Family Number min-max Isotope mole fraction State Relevance
$Fe^{3+}$ Iron(III) cation element 2 constituent element main
$O$ Oxygen element 3.5 constituent element main
$H$ Hydrogen element 1 constituent element main
Composition comments
Common impurities: ?
Oxides
Formula $Fe_{2}O_{3}$ $H_{2}O$
Mass fraction (%) 94.66 5.34

Strunz

Class
oxides - hydroxides - arsenites (04)
Division
hydroxides (without V or U) (04.F)
Family
Hydroxides with OH, without H2O; sheets of edge-sharing octahedral (04.FE)
Code
04.FE.35

Dana

Major class
oxides and hydroxides (III)
Class
simple oxides (04)
Type
with a cation charge of 3+ (A+++2O3) (04.03)
Group
-Ferrihydrite- group (04.03.02)
Code
04.03.02.02
Phase type
crystalline
Crystal system
trigonal
Crystal class
hexagonal-scalenohedral
Crystal class symbol
-3m (D3d)
Crystal spacegroup
P-31c
Texture
nanocrystalline
Molar mass
168.70 $g/mol$
Density
3.8 - 3.93 $g/cm^3$
Refringence type
unknown
Refringence sign
unknown
Color
yellow brown, dark brown
Diaphaneity
opaque
Luster
unknown