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Mineral speciesFormula
 AfwilliteCa3Si2O4(OH)6 
Mineralogy
Family: Thaumasite Group 
Space group: Monoclinic - Sphenoidal H-M Symbol (2) Space Group: P 21 
Dana class: 52.4.7.1 (52 )Nesosilicate Insular SiO4 Groups and O, OH, F, and H2O (52.4) with cations in [6] and/or > [6] coordination (52.4.7) Afwillite and related species 
Geological context
High temperature: Probably related with the weathering. Also as artificial mineral found in the concrete 
Geological context: A product of contact metamorphism of limestones. 
Thermodynamics
Individual properties
Molar weight: 342.447 g/mol  ΔGºf-4,469,061 J/mol ref.  Sº: 289.70 J/mol/K ref. 
  ΔHºf-4,853,820 J/mol ref.  Cp: 303.55 J/mol/K ref. 
Reaction properties
Chemical reaction:  Afwillite + 6H+ = 3Ca+2 + 2H4SiO4 + 2H2O 
log10(Keq) = A + B.T + C.T-1 + D.log10(T) + E.T−2 (with T expressed in Kelvin)
A B C D E
 -9.25484604e+2   -1.38453034e-1   6.20777788e+4   3.37759279e+2   -2.47006385e+6 
Van t'Hoff
@ 25°C, 1 bar: log 10(Keq)49.42
ΔH°r-269,228 J/mol ref.
T (ºC) : 0 25 60 100 150 200 250 300
log 10(Keq):  53.77   49.42   44.52   40.16   35.96   32.68   29.97   27.58 
Maier Kelley
Cp(T) = a + b*10-3T + C*105T-2 (with T expressed in Kelvin)  ref.
a:303.55 J/mol/K 
b:0.00 J/mol/K2 
c:0.00 J.K/mol 

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