Riebeckite

Formula : Na2(Fe3Fe2)Si8O22(OH)2

Family: 
Amphiboles
Space group: 
Monoclinic - Prismatic H-M Symbol (2/m) Space Group: C 2/m
Dana class: 
66.1.3c.5 (66) Inosilicate Double-Width Unbranched Chains, W=2 (66.1) Dana Type (66.1.3c) Group 4, the sodic amphiboles
High temperature: 
According to the published metamorphic grids, the stability of amphibole ranges between 300C to 800C. It depends strongly on the fugacity of water and pressure.
Geological context: 
Occurs in alkalic granites and syenites; rarer in felsic volcanics and granite pegmatites; in some schists. In iron formations as asbestiform "crocidolite". According to the published metamorphic grids, the stability of amphibole ranges between 300C to 800C. It depends strongly on the fugacity of water and pressure.

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
935.900 274.900 (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. -9352433 (Ref.: Internal calculation) -10035550 (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. 691.000 (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. 676.62 (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.
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.
772.10 282.70 -159.80 (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.
Reaction properties

Riebeckite + 14H+ + 8H2O ⇌ 3Fe+2 + 2Na+ + 8H4SiO4

298.15 K, 1 bar log10K: 9.20 ΔH°r:-197377 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 12.07 9.20 5.39 1.81 -1.73 -4.61 -7.22 -9.95
log10K(T) = A + B·T + C·T-1 + D·log10(T) + E·T−2 (T in Kelvin)
A B C D E
-5007.910191 -0.671708 306089.505709 1778.574247 -18686838.774306