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Mineral speciesFormula
 Beidellite(K)K0.34Al2.34Si3.66O10(OH)2 
Mineralogy
Family: Smectite Group 
Space group: Monoclinic - Prismatic HM symbol (2/m) Space Group: C 2/m or ORTH 
Dana class: 71.3.1a.1VIII- 71 Phyllosilicate Minerals ; 71.3 Phyllosilicates Phyllosilicate Sheets of Six-Membered Rings with 2:1 clays ; 71.3.1a Smectite group (Dioctahedral 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 prinicpal constituent of bentonite clay deposits. These have been formed by the alteration of eruptive igneous rocks. They occur in sedimentary and metamorphic rocks, in deposits of hydrothermal origin, and soils, and are useful in the preparation of ceramics, drilling muds, paper, rubber, paints and moulding sands. 
Thermodynamics
Individual properties
Molar weight: 373.232 g/mol  ΔGºf-5,387,734 J/mol ref.  Sº: 265.67 J/mol/K ref. 
  ΔHºf-5,761,310 J/mol ref.  Cp: 310.36 J/mol/K ref. 
Reaction properties
Chemical reaction:  Beidellite(K) + 7.36H+ + 2.64H2O = 2.34Al+3 + 0.34K+ + 3.66H4SiO4 
log10(Keq) = A + B.T + C.T-1 + D.log10(T) + E.T−2 (with T expressed in Kelvin)
A B C D E
 -1.21636920e+3   -1.94629826e-1   7.07744995e+4   4.35362553e+2   -3.34345307e+6 
Van t'Hoff
@ 25°C, 1 bar: log 10(Keq)2.65
ΔH°r-177,653 J/mol ref.
T (ºC) : 0 25 60 100 150 200 250 300
log 10(Keq):  5.48   2.65   -0.63   -3.64   -6.67   -9.22   -11.53   -13.77 
Maier Kelley
Cp(T) = a + b*10-3T + C*105T-2 (with T expressed in Kelvin)  ref.
a:310.36 J/mol/K 
b:0.00 J/mol/K2 
c:0.00 J.K/mol 

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