Goethite

Formula : FeOOH

Family: 
Hydroxides
Space group: 
Orthorhombic - Dipyramidal HM symbol (2/m 2/m 2/m) Space Group: Pbnm
Dana class: 
6.1.1.2VI - 6 Hydroxides and Oxides Containing Hydroxyl ; 6.1 Hydroxides and Oxides Containing Hydroxyl where X+++O OH ; 6.1.1 Diaspore group (Orthorhombic, Pnma or Pnmd)
High temperature: 
In the presence of pure water goethite is stable at all temperatures between OC to 100C. Well crystallized goethite gives a d.t.a. curve with a single endothermic peak at a temperature of 350C to 390C.
Geological context: 
Goethite is a very common mineral typically occurring as a weathering product of iron-bearing minerals such as siderite, magnetite, pyrite, etc. It is normally formed under oxidizing conditions.

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
88.854 20.820 (Ref.: 95rob/hem) Robie R.A., and Hemingway B.S., 1995. Thermodynamic properties of minerals and related substances at 298.15 K and 1 Bar (105 Pascals) pressure and at higher temperatures. U.S. Geol. Survey Bull., 2131, 461 pp. -488506 (Ref.: 95par/kho) Parker, V.B., Khodakovsky, I.L. (1995) Thermodynamic properties of aqueous ions (2+ et 3+) of iron and the key compouds of iron. J. Phys. Chem. Ref. Data 24 (5) p. 1699-1745. -560000 (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. 58.019 (Ref.: Internal calculation) 74.31 (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.
1.25 233.20 3.14 (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

Goethite + 3H+ ⇌ Fe+3 + 2H2O

298.15 K, 1 bar log10K: 0.36 ΔH°r:-60660 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 1.33 0.36 -0.75 -1.77 -2.79 -3.66 -4.47 -5.29
log10K(T) = A + B·T + C·T-1 + D·log10(T) + E·T−2 (T in Kelvin)
A B C D E
-496.871073 -0.081270 27746.417060 178.977899 -1286057.524682