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Mineral speciesFormula
 Ferrihydrite(6L)Fe(OH)3 
Mineralogy
Space group: Trigonal - Hexagonal Scalenohedral HM symbol (-3 2/m) Space Group: P 31c 
Dana class: 4.3.2.2III - 4 Oxide Minerals ; 4.3 Simple Oxides with a cation charge of 3+ (A+++2 O3) ; 4.3.2 
Geological context
Geological context: Widespread in the soluble fraction of soils and weathered rock. In precipitates around cold and hot springs, especially those supporting iron-metabolizing bacteria; in acid mine effluent. 
Thermodynamics
Individual properties
Molar weight: 106.869 g/mol  ΔGºf-710,577 J/mol ref.  Sº: 129.52 J/mol/K ref. 
  ΔHºf-830,300 J/mol ref.  Cp: 101.67 J/mol/K ref. 
Reaction properties
Chemical reaction:  Ferrihydrite(6L) + 3H+ = Fe+3 + 3H2O 
log10(Keq) = A + B.T + C.T-1 + D.log10(T) + E.T−2 (with T expressed in Kelvin)
A B C D E
 -4.82892187e+2   -7.37666900e-2   2.81925316e+4   1.72735435e+2   -1.25268739e+6 
Van t'Hoff
@ 25°C, 1 bar: log 10(Keq)3.00
ΔH°r22,692 J/mol ref.
T (ºC) : 0 25 60 100 150 200 250 300
log 10(Keq):  4.23   3.00   1.62   0.39   -0.79   -1.74   -2.56   -3.35 
Maier Kelley
Cp(T) = a + b*10-3T + C*105T-2 (with T expressed in Kelvin)  ref.
a:101.67 J/mol/K 
b:0.00 J/mol/K2 
c:0.00 J.K/mol 

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