Cummingtonite

Formula : Mg7Si8O22(OH)2

Family: 
Amphiboles
Space group: 
Monoclinic - Prismatic H-M Symbol (2/m) Space Group: C 2/m
Dana class: 
66.1.1.2 (66)Inosilicate Double-Width Unbranched Chains, W=2 (66.1) Dana Type (66.1.1) Group 1, the Mg-Fe-Mn-Li amphiboles (Monoclinic)
High temperature: 
The stability domain ranges roughly from 550C to 800C. It depends on aH2O, aCO2,...
Geological context: 
Contact and regional metamorphic rocks.

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
780.820 271.900 (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. -11329836 (Ref.: Internal calculation) -12056790 (Ref.: 98hol/pow) Holland T.J.B., and Powell R., 1998. An internally consistent thermodynamic data set for phases of petrological interest. Journal of Metamorphic Geology, 16, p. 309 343. 533.460 (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. 637.95 (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.
775.04 245.22 -186.86 (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

Cummingtonite + 14H+ + 8H2O ⇌ 7Mg+2 + 8H4SiO4

298.15 K, 1 bar log10K: 76.15 ΔH°r:-596457 J·mol-1 (Ref.: 98hol/pow) Holland T.J.B., and Powell R., 1998. An internally consistent thermodynamic data set for phases of petrological interest. Journal of Metamorphic Geology, 16, p. 309 343.
T(°C) 0 25 60 100 150 200 250 300
log10K 85.43 76.15 65.02 54.81 44.81 36.89 30.22 24.16
log10K(T) = A + B·T + C·T-1 + D·log10(T) + E·T−2 (T in Kelvin)
A B C D E
-5242.144204 -0.699987 339797.658432 1861.186296 -19385351.046190