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Mineral speciesFormula
 GreigiteFe3S4 
Mineralogy
Space group: Isometric - Hexoctahedral HM symbol (4/m -3 2/m) Space Group: F d3m 
Dana class: 2.10.1.10II- 2 Sulfide Minerals ; 2.10 Sulfides - Including Selenides and Tellurides where Am Bn Xp, with (m+n):p=3:4 ; 2.10.1 Linnaeite Group (Isometric: Fd3m) 
Geological context
Geological context: Formed in lacustrine beds consisting of interbedded calcareous clays, silts, and fine- to medium-grained arkosic sands; in varvelike laminae of grayish black sulfide-bearing clays and fine silts; possibly as the result of seasonal variation in the composition and physical condition of lake waters; also in hydrothermal vein deposits; formed in magnetotactic bacteria, and by sulfate-reducing bacteria. 
Thermodynamics
Individual properties
Molar weight: 295.805 g/mol  ΔGºf-306,433 J/mol ref.  Sº: 194.82 J/mol/K ref. 
  ΔHºf-311,011 J/mol ref.   
Reaction properties
Chemical reaction:  Greigite + 2H+ + 0.75H2O = 3Fe+2 + 3.5HS- + 0.25S2O3-2 
log10(Keq) = A + B.T + C.T-1 + D.log10(T) + E.T−2 (with T expressed in Kelvin)
A B C D E
 -3.55439809e+3   -5.61876813e-1   1.91106081e+5   1.28781730e+3   -1.13392773e+7 
Van t'Hoff
@ 25°C, 1 bar: log 10(Keq)-21.89
ΔH°r-3,219,517 J/mol ref.
T (ºC) : 0 25 60 100 150 200 250 300
log 10(Keq):  -22.58   -21.89   -21.38   -21.20   -21.41   -22.09   -23.32   -25.38 

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