Talc

Formula : Mg3Si4O10(OH)2

Space group: 
Monoclinic - Prismatic H-M Symbol (2/m) Space Group: C 2/c
Dana class: 
71.2.1.3 (71) Phyllosilicate Sheets of Six-Membered Rings (71.2)with 2:1 Layers (71.2.1)Pyrophyllite-talc group
High temperature: 
The temperature stability range of talc is large from room-temperature to around 700C. It depends on the chemistry of rock, the water fugacity, the CO2 fugacity, of the pressure.
Geological context: 
In talc-rich schists or steatite through hydrothermal alteration of mafic rocks (steatitization) subsequent to serpentinization during greenschist facies metamorphism. Also formed by thermal low-temperature metamorphism of siliceous dolostones.

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
379.266 136.250 (Ref.: 78hel/del) Helgeson, H.C., Delany, J.M, Nesbitt, H.W., and Bird, D.K., 1978. Summary and Critique of the Thermodynamic Properties of Rock Forming Minerals: Amer. J. Sci., 278A, 229 pp. -5512253 (Ref.: Internal calculation) -5892100 (Ref.: 01kal/mar) Kahl W.A. and Maresch W.V., 2001. Enthalpies of formation of tremolite and talc by high-temperature solution calorimetry-a consistent picture. American Mineralogist, 86, p. 1345-1357 260.831 (Ref.: 63rob/sto) Robie, R. A., and J. W. Stout, 1963. Heat capacity from 12 to 305K and entropy of talc and tremolite. J. Phys. Chem., 57, p. 2252-2256 320.59 (Ref.: 79kru/rob) >Krupka, K.M., Robie, R.A., Hemingway, B.S., 1979. High-temperatur heat capacities of corundum, periclas, anorthite, CaAl2S2O8 glass, muscovite, pyrophyllite, KAlSi3O8 glass, grossular and NaAlSi3O8 glass. Am. Mineral., 64, p. 86-101
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.
420.72 90.46 -112.98 (Ref.: 79kru/rob) >Krupka, K.M., Robie, R.A., Hemingway, B.S., 1979. High-temperatur heat capacities of corundum, periclas, anorthite, CaAl2S2O8 glass, muscovite, pyrophyllite, KAlSi3O8 glass, grossular and NaAlSi3O8 glass. Am. Mineral., 64, p. 86-101
Reaction properties

Talc + 6H+ + 4H2O ⇌ 3Mg+2 + 4H4SiO4

298.15 K, 1 bar log10K: 24.93 ΔH°r:-201024 J·mol-1 (Ref.: 01kal/mar) Kahl W.A. and Maresch W.V., 2001. Enthalpies of formation of tremolite and talc by high-temperature solution calorimetry-a consistent picture. American Mineralogist, 86, p. 1345-1357
T(°C) 0 25 60 100 150 200 250 300
log10K 28.01 24.93 21.16 17.68 14.30 11.61 9.34 7.22
log10K(T) = A + B·T + C·T-1 + D·log10(T) + E·T−2 (T in Kelvin)
A B C D E
-2424.182571 -0.320735 154357.525310 860.545252 -9097220.153547