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Mineral speciesFormula
 Ettringite(Cr)Ca6Al2(OH)12(CrO4)3:26H2O 
Mineralogy
Family: Ettringite Group 
Space group: Hexagonal - Dihexagonal Dipyramidal H-M Symbol (6/m 2/m 2/m) Space Group: P 63/mmc 
Dana class: 31.10.2.1 (31) Hydrated Sulfates Containing Hydroxyl or Halogen (31.10) miscellaneous (31.10.2)Dana Group  
Geological context
High temperature: Chromium analog to ettringite 
Geological context: see ettringite 
Thermodynamics
Individual properties
Molar weight: 1,314.807 g/mol  ΔGºf-15,132,198 J/mol ref.  Sº: 2,315.11 J/mol/K ref. 
  ΔHºf-17,330,292 J/mol ref.  Cp: 2,120.00 J/mol/K ref. 
Reaction properties
Chemical reaction:  Ettringite(Cr) + 12H+ = 2Al+3 + 6Ca+2 + 3CrO4-2 + 38H2O 
log10(Keq) = A + B.T + C.T-1 + D.log10(T) + E.T−2 (with T expressed in Kelvin)
A B C D E
 -6.46282378e+3   -1.00295739e+0   3.73727964e+5   2.34086195e+3   -1.98824278e+7 
Van t'Hoff
@ 25°C, 1 bar: log 10(Keq)60.28
ΔH°r-503,048 J/mol ref.
T (ºC) : 0 25 60 100 150 200 250 300
log 10(Keq):  68.23   60.28   50.92   42.17   33.20   25.49   18.25   10.59 
Maier Kelley
Cp(T) = a + b*10-3T + C*105T-2 (with T expressed in Kelvin)  ref.
a:2,120.00 J/mol/K 
b:0.00 J/mol/K2 
c:0.00 J.K/mol 

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