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Mineral speciesFormula
 Chalcocite(alpha)Cu2S 
Mineralogy
Family: Chalcocite - Yarrowite series 
Space group: Monoclinic - Prismatic H-M Symbol (2/m) Space Group: P 21/c 
Dana class: 2.4.7.1 (2) Sulfides - Including Selenides and Tellurides (2.4) where Am Bn Xp, with (m+n):p=2:1(2.4.7) Chalcocite Group ([Cu]2-x S] formulae) 
Geological context
High temperature: Chalcocite is stable under a normal atmospheric conditions. 
Geological context: Secondary mineral in or near the oxidized zone of copper sulfide deposits. 
Thermodynamics
Individual properties
Molar weight: 159.158 g/mol  ΔGºf-86,223 J/mol ref.  Sº: 120.92 J/mol/K ref. 
  ΔHºf-79,496 J/mol ref.  Cp: 76.32 J/mol/K ref. 
Reaction properties
Chemical reaction:  Chalcocite(alpha) + H+ = 2Cu+ + HS- 
log10(Keq) = A + B.T + C.T-1 + D.log10(T) + E.T−2 (with T expressed in Kelvin)
A B C D E
 -8.83796573e+2   -1.39688509e-1   3.70797559e+4   3.22830418e+2   -2.88893943e+6 
Van t'Hoff
@ 25°C, 1 bar: log 10(Keq)-34.75
ΔH°r-953,897 J/mol ref.
T (ºC) : 0 25 60 100 150 200 250 300
log 10(Keq):  -38.38   -34.75   -30.67   -27.01   -23.50   -20.86   -18.88   -17.51 
Maier Kelley
Cp(T) = a + b*10-3T + C*105T-2 (with T expressed in Kelvin)  ref.
a:52.84 J/mol/K 
b:78.74 J/mol/K2 
c:0.00 J.K/mol 

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