Sillimanite

Formula : Al2SiO5

Space group: 
Orthorhombic - DipyramidalH-M Symbol (2/m 2/m 2/m) Space Group: P nma
Dana class: 
52.2.2a.1 (52) Nesosilicate Insular SiO4 Groups and O, OH, F, and H2O (52.2) with cations in [4] and >[4] coordination (52.2.2a) Al2SiO5 (Sillimanite subgroup)
High temperature: 
Lower limit of stability aroud 500C.
Geological context: 
Of widespread occurrence. In high-grade metamorphic schists, gneisses, and hornfels; more rarely in pegmatites.

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
162.046 49.900 (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. -2427101 (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. -2573646 (Ref.: Internal calculation) 96.776 (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. 121.73 (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.
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.
167.46 30.92 -48.84 (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.
Reaction properties

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

298.15 K, 1 bar log10K: 16.57 ΔH°r:-247845 J·mol-1 (Ref.: Internal calculation)
T(°C) 0 25 60 100 150 200 250 300
log10K 20.48 16.57 11.95 7.65 3.29 -0.34 -3.53 -6.48
log10K(T) = A + B·T + C·T-1 + D·log10(T) + E·T−2 (T in Kelvin)
A B C D E
-1342.888471 -0.205134 85642.986819 477.747735 -4336623.817198