Hmontmorillonite(MgCa)

Formula : Ca0.17Mg0.34Al1.66Si4O10(OH)2:4.265H2O

Space group: 
Monoclinic - Prismatic HM symbol (2/m) Space Group: C 2/m
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)
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.

Dernière mise à jour le 25.01.2021

THERMODYNAMICS

Individual properties (298.15 K)
M
g·mol-1
 V°
cm3·mol-1
 ΔGºf
J·mol-1
 ΔHºf
J·mol-1
 Sº
J·mol-1·k-1
 CP
J·mol-1·K-1
443.052 212.648 (Ref.: 15bla/vie, 11vie/bla) -6347546 (Ref.: Internal calculation) -6940594 (Ref.: 15bla/vie, 11vie/bla) 507.731 (Ref.: 15bla/vie, 11vie/bla) 626.30 (Ref.: 15bla/vie, 11vie/bla)
CP(T) = a + b·T + ·c·T-2 (T in Kelvin)
a
J·mol-1·K-1
 b * 103
J·mol-1·K-2
 c * 10-5
J·K·mol-1
 Maier Kelley Ref.
626.31 0.00 0.00 (Ref.: 15bla/vie, 11vie/bla)
Reaction properties

Hmontmorillonite(MgCa) + 6H+ ⇌ 1.66Al+3 + 0.17Ca+2 + 0.34Mg+2 + 4H4SiO4

298.15 K, 1 bar log10K: 1.86 ΔH°r:-115428 J·mol-1 (Ref.: 15bla/vie, 11vie/bla)
T(°C) 0 25 60 100 150 200 250 300
log10K 3.54 1.86 -0.39 -2.55 -4.75 -6.57 -8.20 -9.82
log10K(T) = A + B·T + C·T-1 + D·log10(T) + E·T−2 (T in Kelvin)
A B C D E
-2313.067487 -0.307857 144465.332757 817.500029 -8949378.765906