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Mineral speciesFormula
 EpidoteCa2FeAl2Si3O12(OH) 
Mineralogy
Family: Epidote Group 
Space group: Monoclinic - Prismatic H-M Symbol (2/m) Space Group: P 21/m 
Dana class: 58.2.1a.7 (58) Sorosilicate Insular, Mixed, Single, and Larger Tetrahedral Groups (58.2 )with cations in [6] and higher coordination; single and double groups (n=1,2) (58.2.1a) Epidote group (Epidote subgroup) 
Geological context
High temperature: Temperature stability range between 240-300C to 700C. 
Geological context: Epidote (Pistacite), occurs chiefly in regionally metamorphosed igneous and sedimentary rocks; in acid rocks contaminated by calc-silicate materials; as an alteration of plagioclase. 
Thermodynamics
Individual properties
Molar weight: 483.223 g/mol  ΔGºf-6,070,591 J/mol ref.  Sº: 314.97 J/mol/K ref. 
  ΔHºf-6,460,388 J/mol ref.  Cp: 358.14 J/mol/K ref. 
Reaction properties
Chemical reaction:  Epidote + 13H+ = 2Al+3 + 2Ca+2 + Fe+3 + 3H4SiO4 + H2O 
log10(Keq) = A + B.T + C.T-1 + D.log10(T) + E.T−2 (with T expressed in Kelvin)
A B C D E
 -1.96009815e+3   -3.24526771e-1   1.19082402e+5   7.06721747e+2   -5.13382849e+6 
Van t'Hoff
@ 25°C, 1 bar: log 10(Keq)33.53
ΔH°r-321,943 J/mol ref.
T (ºC) : 0 25 60 100 150 200 250 300
log 10(Keq):  40.27   33.53   25.78   18.67   11.52   5.58   0.33   -4.63 
Maier Kelley
Cp(T) = a + b*10-3T + C*105T-2 (with T expressed in Kelvin)  ref.
a:492.13 J/mol/K 
b:53.62 J/mol/K2 
c:-133.32 J.K/mol 

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