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Mineral speciesFormula
 DiopsideCaMg(SiO3)2 
Mineralogy
Family: Pyroxene Group 
Space group: Monoclinic - Prismatic H-M Symbol (2/m) Space Group: C 2/c 
Dana class: 65.1.3a.1 (65) Inosilicate Single-Width Unbranched Chains, W=1(65.1)with chains P=2 (65.1.3a)C2/c clinopyroxenes (Ca clinopyroxenes) 
Geological context
High temperature: The minimal stability temperature of diopside can be estimated around 550C but this latter is strongly dependant on aH2O,aCO2. 
Geological context: Basic and ultrabasic igneous and metamorphic rocks. 
Thermodynamics
Individual properties
Molar weight: 216.550 g/mol  ΔGºf-3,028,296 J/mol ref.  Sº: 143.09 J/mol/K ref. 
  ΔHºf-3,202,488 J/mol ref.  Cp: 156.90 J/mol/K ref. 
Reaction properties
Chemical reaction:  Diopside + 4H+ + 2H2O = Ca+2 + Mg+2 + 2H4SiO4 
log10(Keq) = A + B.T + C.T-1 + D.log10(T) + E.T−2 (with T expressed in Kelvin)
A B C D E
 -6.78805763e+2   -1.06778584e-1   4.27463731e+4   2.46223653e+2   -1.80123014e+6 
Van t'Hoff
@ 25°C, 1 bar: log 10(Keq)21.73
ΔH°r-158,241 J/mol ref.
T (ºC) : 0 25 60 100 150 200 250 300
log 10(Keq):  24.28   21.73   18.84   16.23   13.68   11.62   9.86   8.24 
Maier Kelley
Cp(T) = a + b*10-3T + C*105T-2 (with T expressed in Kelvin)  ref.
a:221.21 J/mol/K 
b:32.80 J/mol/K2 
c:-65.86 J.K/mol 

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