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Mineral speciesFormula
 Almandine(alpha)Fe3Al2Si3O12 
Mineralogy
Family: Garnet Group 
Space group: Isometric - Hexoctahedral H-M Symbol (4/m 3 2/m) Space Group: I a3d 
Dana class: 51.4.3a.2 (51)Nesosilicate Insular SiO4 Groups Only (51.4) with cations in [6] and >[6] coordination (51.4.3a) Garnet group (Pyralspite series) 
Geological context
High temperature: Based on the garnet stability, almandine may be stable around 500C and less with the increase of pressure. 
Geological context: The most common garnet, typically in mica schists and gneisses, from regionally metamorphosed argillaceous sediments and pelites; also in contact metamorphic hornfels and in granites and eclogites. 
Thermodynamics
Individual properties
Molar weight: 497.753 g/mol  ΔGºf-4,933,875 J/mol ref.  Sº: 316.31 J/mol/K ref. 
  ΔHºf-5,264,700 J/mol ref.  Cp: 361.83 J/mol/K ref. 
Reaction properties
Chemical reaction:  Almandine(alpha) + 12H+ = 2Al+3 + 3Fe+2 + 3H4SiO4 
log10(Keq) = A + B.T + C.T-1 + D.log10(T) + E.T−2 (with T expressed in Kelvin)
A B C D E
 -2.05734018e+3   -3.30744621e-1   1.29093427e+5   7.39385591e+2   -5.72715780e+6 
Van t'Hoff
@ 25°C, 1 bar: log 10(Keq)42.16
ΔH°r-465,683 J/mol ref.
T (ºC) : 0 25 60 100 150 200 250 300
log 10(Keq):  49.61   42.16   33.58   25.69   17.79   11.28   5.59   0.32 
Maier Kelley
Cp(T) = a + b*10-3T + C*105T-2 (with T expressed in Kelvin)  ref.
a:408.02 J/mol/K 
b:140.75 J/mol/K2 
c:-78.37 J.K/mol 

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