Kaolinite

Formula : Al2Si2O5(OH)4

Space group: 
Triclinic - Pedial H-M Symbol (1) Space Group: P1
Dana class: 
71.1.1.2 (71) Phyllosilicate Sheets of Six-Membered Rings (71.1) with 1:1 layers (71.1.1) Kaolinite group
High temperature: 
This mineral is stable from the room temperature up to 260C in hydrothermal systems.
Geological context: 
Secondary mineral derived from the wathering of alumino-silicate mineral and also from hydrothermal alteration. Replaces other aluminosilicate minerals during hydrothermal alteration and weathering. A common constituent of the clay-size fraction of sediments, where it may be formed by direct precipitation.

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
258.160 99.340 (Ref.: 95rob/hem) Robie R.A., and Hemingway B.S., 1995. Thermodynamic properties of minerals and related substances at 298.15 K and 1 Bar (105 Pascals) pressure and at higher temperatures. U.S. Geol. Survey Bull., 2131, 461 pp. -3793935 (Ref.: Internal calculation) -4115300 (Ref.: 01fia/nav) Fialips C.-I., Navrotsky A. and Petit S. (2001) - Crystal properties and energetics of synthetic kaolinite. American Mineralogist, 86, p. 304.311. 200.900 (Ref.: 91rob/hem) Robie R.A. and Hemingway B.S. (1991) - Heat capacities of kaolinite from 7 to 380 K and of DSMO-intercalated kaolinite AI2Si20 (OH). Clays and Clay Minerals, 39, p. 362-368 243.37 (Ref.: 91rob/hem) Robie R.A. and Hemingway B.S. (1991) - Heat capacities of kaolinite from 7 to 380 K and of DSMO-intercalated kaolinite AI2Si20 (OH). Clays and Clay Minerals, 39, p. 362-368
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.
277.18 130.42 -64.62 (Ref.: 91rob/hem) Robie R.A. and Hemingway B.S. (1991) - Heat capacities of kaolinite from 7 to 380 K and of DSMO-intercalated kaolinite AI2Si20 (OH). Clays and Clay Minerals, 39, p. 362-368
Reaction properties

Kaolinite + 6H+ ⇌ 2Al+3 + 2H4SiO4 + H2O

298.15 K, 1 bar log10K: 6.48 ΔH°r:-165052 J·mol-1 (Ref.: 01fia/nav) Fialips C.-I., Navrotsky A. and Petit S. (2001) - Crystal properties and energetics of synthetic kaolinite. American Mineralogist, 86, p. 304.311.
T(°C) 0 25 60 100 150 200 250 300
log10K 9.04 6.48 3.38 0.48 -2.45 -4.91 -7.12 -9.24
log10K(T) = A + B·T + C·T-1 + D·log10(T) + E·T−2 (T in Kelvin)
A B C D E
-1661.404685 -0.240262 102021.658626 590.679617 -5712177.646033