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Table 2 Gibbs free energies of low temperature iron and silica oxyhydroxides in the system Fe–Si–O–H at 25°C and 1 bar

From: Microbial and hydrothermal aspects of ferric oxyhydroxides and ferrosic hydroxides: the example of Franklin Seamount, Western Woodlark Basin, Papua New Guinea

  Sadiq and Lindsay, 1979 (ref. 39) kcal mole-1 Ponamperuma et al., 1967 (ref 25) kcal mole -1 Langmuir, 1969 (ref. 360) kcal mole-1 Winters and Buckley, 1986 (ref. 43) kcal mole-1 SUPCRT92, Johnson et al., 1991 (ref. 19) kcal mole -1
Fe3+ (aq) -4.02 -- -4.02 -- -4.12
Fe2+ (aq) -21.80 -20.3 -21.8 -18.85 -21.87
Fe(OH)2 (s) -117.584 -115.6 -117.584 -116.3  
Fe(OH)3 (s) soil amorphous ferric iron -170.250 -- -- -- --
Fe(OH)3 (s) aged amorphous ferric iron -170.163 -- -- -- --
Fe(OH)3 (s) 4 day old amorphous ferric iron -169.250 -- -169.040 -- --
Fe(OH)3 (s) freshly precipitated amorphous ferric iron Nature uncertain -166.0 -167.460 -166.5 --
Fe3(OH)8 (s) freshly precipitated amorphous mixed-valence iron -459.220 -451.2 (nature uncertain) -- -- --
H2O -56.687 -56.7 -56.688 -56.69 -56.688
OH- -37.594 -- -37.594 -- -37.595
SiO2 amorphous -203.02 -- -- -202.89 -202.89 (SiO2- nH20)
Ferrosilite -257.6 -- -- -267.16 -267.16
Si(OH)4 (aq) -312.66 -- -- -- -312.6 (SiO2 [aq)]