Maghemite(disordered)

Formula : Fe2O3

Family: 
Oxides
Space group: 
Isometric - Tetartoidal HM symbol (2 3) Space Group: P 213
Dana class: 
4.3.7.1III - 4 Oxide Minerals ; 4.3 Simple Oxides with a cation charge of 3+ (A+++2 O3) ; 4.3.7
High temperature: 
Stable at room temperature and in in low temperature hydrothermal systems
Geological context: 
Formed by weathering or low-temperature oxidation of spinels containing ferrous iron, commonly magnetite or titanian magnetite. Widespread yellow pigment in sediments.

Dernière mise à jour le 25.01.2021

THERMODYNAMICS

Individual properties (298.15 K)
M
g·mol-1
 V°
cm3·mol-1
 ΔGºf
J·mol-1
 ΔHºf
J·mol-1
 Sº
J·mol-1·k-1
 CP
J·mol-1·K-1
159.692 29.087 (Ref.: 63wyc) Wyckoff, R.W.G., 1963, Crystal Structures, Second edition, tome 4, Interscience Publishers, New York, p. 320-322. -727788 (Ref.: Internal calculation) -808100 (Ref.: 03maj/gre) Majzlan., J., Grevel, K.-D., Navrotsky, A., (2003) Thermodynamics of iron oxides. H. Enthalpies of formation and relative stability of goethite (a-FeOOH), lepidocrocite (y-FeOOH), and maghemite (y-Fe2O3). American Mineralogist 88, 855-859. 93.000 (Ref.: 03maj/gre) Majzlan., J., Grevel, K.-D., Navrotsky, A., (2003) Thermodynamics of iron oxides. H. Enthalpies of formation and relative stability of goethite (a-FeOOH), lepidocrocite (y-FeOOH), and maghemite (y-Fe2O3). American Mineralogist 88, 855-859. 104.99 (Ref.: 03maj/gre) Majzlan., J., Grevel, K.-D., Navrotsky, A., (2003) Thermodynamics of iron oxides. H. Enthalpies of formation and relative stability of goethite (a-FeOOH), lepidocrocite (y-FeOOH), and maghemite (y-Fe2O3). American Mineralogist 88, 855-859.
CP(T) = a + b·T + ·c·T-2 (T in Kelvin)
a
J·mol-1·K-1
 b * 103
J·mol-1·K-2
 c * 10-5
J·K·mol-1
 Maier Kelley Ref.
106.80 65.09 -18.86 (Ref.: 03maj/gre) Majzlan., J., Grevel, K.-D., Navrotsky, A., (2003) Thermodynamics of iron oxides. H. Enthalpies of formation and relative stability of goethite (a-FeOOH), lepidocrocite (y-FeOOH), and maghemite (y-Fe2O3). American Mineralogist 88, 855-859.
Reaction properties

Maghemite(disordered) + 6H+ ⇌ 2Fe+3 + 3H2O

298.15 K, 1 bar log10K: 2.84 ΔH°r:-147390 J·mol-1 (Ref.: 03maj/gre) Majzlan., J., Grevel, K.-D., Navrotsky, A., (2003) Thermodynamics of iron oxides. H. Enthalpies of formation and relative stability of goethite (a-FeOOH), lepidocrocite (y-FeOOH), and maghemite (y-Fe2O3). American Mineralogist 88, 855-859.
T(°C) 0 25 60 100 150 200 250 300
log10K 5.20 2.84 0.13 -2.36 -4.87 -6.98 -8.88 -10.73
log10K(T) = A + B·T + C·T-1 + D·log10(T) + E·T−2 (T in Kelvin)
A B C D E
-947.107438 -0.153373 54980.194207 339.363811 -2530123.851301