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Mineral speciesFormula
 Coesite(alpha)SiO2 
Mineralogy
Family: Quartz Group 
Space group: Monoclinic - Prismatic H-M Symbol (2/m) Space Group: C 2/c 
Dana class: 75.1.4.1 (75) Tectosilicate Si Tetrahedral Frameworks(75.1) SiO2 with [4] coordinated Si (75.1.4) Dana Group 
Geological context
High temperature: Coesite is a high presure mineral its stability is limited by stishovite (an other silica polymorph) at about 65 kbar. 
Geological context: Formed at pressures in excess of 20 kbar, as fine-grained intergrowths with quartz and silica glass in impact metamorphosed rocks and tektites. A primary phase in grospydite (kyanite-garnet-clinopyroxene) xenoliths in kimberlite, and intergrown with quartz as inclusions in garnet and clinopyroxene within eclogites of high-grade metamorphic terranes. 
Thermodynamics
Individual properties
Molar weight: 60.084 g/mol  ΔGºf-851,577 J/mol ref.  Sº: 40.38 J/mol/K ref. 
  ΔHºf-906,313 J/mol ref.  Cp: 43.54 J/mol/K ref. 
Reaction properties
Chemical reaction:  Coesite(alpha) + 2H2O = H4SiO4 
log10(Keq) = A + B.T + C.T-1 + D.log10(T) + E.T−2 (with T expressed in Kelvin)
A B C D E
 -1.92947953e+1   -3.55323192e-3   -1.26920316e+2   7.30095821e+0   -1.79183872e+4 
Van t'Hoff
@ 25°C, 1 bar: log 10(Keq)-2.92
ΔH°r16,779 J/mol ref.
T (ºC) : 0 25 60 100 150 200 250 300
log 10(Keq):  -3.18   -2.92   -2.60   -2.31   -2.02   -1.79   -1.61   -1.47 
Maier Kelley
Cp(T) = a + b*10-3T + C*105T-2 (with T expressed in Kelvin)  ref.
a:46.02 J/mol/K 
b:34.31 J/mol/K2 
c:-11.30 J.K/mol 

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