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Mineral speciesFormula
 EttringiteCa6Al2(SO4)3(OH)12:26H2O 
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: The upper stability of this mineral is limited around 60C to 90C. 
Geological context: Related to the leaching of contact metamorphism halos in marl or natural cements present in the rock at Maqarin in Jordan. Layers of bituminous marlstone burned at one point in time. Bitumen is a natural form of asphalt, and marlstone is a kind of clay-bearing limestone. Also found in concrete. 
Thermodynamics
Individual properties
Molar weight: 1,255.107 g/mol  ΔGºf-15,210,277 J/mol ref.  Sº: 1,883.75 J/mol/K ref. 
  ΔHºf-17,544,526 J/mol ref.  Cp: 2,174.36 J/mol/K ref. 
Reaction properties
Chemical reaction:  Ettringite + 12H+ = 2Al+3 + 6Ca+2 + 3SO4-2 + 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
 -6.67460197e+3   -1.04743390e+0   3.78708023e+5   2.42662966e+3   -2.05189885e+7 
Van t'Hoff
@ 25°C, 1 bar: log 10(Keq)57.01
ΔH°r-379,834 J/mol ref.
T (ºC) : 0 25 60 100 150 200 250 300
log 10(Keq):  62.97   57.01   49.89   43.16   36.08   29.78   23.57   16.64 
Maier Kelley
Cp(T) = a + b*10-3T + C*105T-2 (with T expressed in Kelvin)  ref.
a:1,939.12 J/mol/K 
b:789.00 J/mol/K2 
c:0.00 J.K/mol 

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