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Mineral speciesFormula
 BeidelliteSBIdCa0.185K0.104(Si3.574Al0.426)(Al1.812Mg0.090Fe0.112)O10(OH)2 
Mineralogy
Family: Smectite Group 
Space group: Monoclinic - Prismatic HM symbol (2/m) Space Group: C 2/m 
Dana class: 71.3.1b.2VIII- 71 Phyllosilicate Minerals ; 71.3 Phyllosilicates Phyllosilicate Sheets of Six-Membered Rings with 2:1 clays ; 71.3.1b Smectite group (Trioctahedral Smectites) 
Geological context
High temperature: Low temperature mineral. At higher temperatures(> 500C), detachment of (OH) ions takes place. 
Geological context: Montmorillonite and beidellite are the principal constituents of bentonite clay deposits. Montmorillonite results from the weathering of basic rocks mainly in conditionsof poordrainage when magnesium is not removed. 
Thermodynamics
Individual properties
Molar weight: 374.694 g/mol  ΔGºf-5,357,229 J/mol ref.  Sº: 293.52 J/mol/K ref. 
  ΔHºf-5,720,690 J/mol ref.  Cp: 318.50 J/mol/K ref. 
Reaction properties
Chemical reaction:  BeidelliteSBId + 7.704H+ + 2.296H2O = 2.238Al+3 + 0.185Ca+2 + 0.112Fe+3 + 0.104K+ + 0.09Mg+2 + 3.574H4SiO4 
log10(Keq) = A + B.T + C.T-1 + D.log10(T) + E.T−2 (with T expressed in Kelvin)
A B C D E
 -1.28483280e+3   -2.13033882e-1   7.51326928e+4   4.61449247e+2   -3.36869570e+6 
Van t'Hoff
@ 25°C, 1 bar: log 10(Keq)7.58
ΔH°r-213,413 J/mol ref.
T (ºC) : 0 25 60 100 150 200 250 300
log 10(Keq):  11.16   7.58   3.44   -0.38   -4.25   -7.51   -10.46   -13.30 
Maier Kelley
Cp(T) = a + b*10-3T + C*105T-2 (with T expressed in Kelvin)  ref.
a:270.93 J/mol/K 
b:342.91 J/mol/K2 
c:-48.60 J.K/mol 

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