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Mineral speciesFormula
 GehleniteCa2(Al2Si)O7 
Mineralogy
Family: Melilite Group 
Space group: Tetragonal - Scalenohedral H-M Symbol (4 2m) Space Group: P 421m 
Dana class: 55.4.1.2 (55)Sorosilicate Si2O7 Groups, Generally with No Additional Anions (55.4) with cations in [8] and lower coordination (55.4.1) Melilite group 
Geological context
High temperature: High temperature mineral from around 780C to 1600C 
Geological context: Contact metamorphic mineral in limestone. Skarns along the contact of a diorite intrusion . Mineral also found in metallurgical slags and incineration byproducts from municipal solid waste (bottom ash, fly ash). 
Thermodynamics
Individual properties
Molar weight: 274.200 g/mol  ΔGºf-3,786,276 J/mol ref.  Sº: 210.10 J/mol/K ref. 
  ΔHºf-3,985,000 J/mol ref.  Cp: 206.40 J/mol/K ref. 
Reaction properties
Chemical reaction:  Gehlenite + 10H+ = 2Al+3 + 2Ca+2 + H4SiO4 + 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
 -1.47563930e+3   -2.43660303e-1   9.97199735e+4   5.30959338e+2   -3.97935344e+6 
Van t'Hoff
@ 25°C, 1 bar: log 10(Keq)55.23
ΔH°r-496,484 J/mol ref.
T (ºC) : 0 25 60 100 150 200 250 300
log 10(Keq):  63.17   55.23   46.08   37.66   29.25   22.37   16.46   11.11 
Maier Kelley
Cp(T) = a + b*10-3T + C*105T-2 (with T expressed in Kelvin)  ref.
a:227.25 J/mol/K 
b:89.00 J/mol/K2 
c:-42.12 J.K/mol 

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