Annite

Formula : KFe3(AlSi3)O10(OH)2

Space group: 
Monoclinic - Prismatic H-M Symbol (2/m) Space Group: C 2/m
Dana class: 
71.2.2b.3 (71)Phyllosilicate Sheets of Six-Membered Rings (71.2)with 2:1 Layers (71.2.2b) Mica Group (Biotite subgroup)
High temperature: 
Stable to250 to 600C in hydrothermal systems, above 1000C for meamorphic events.
Geological context: 
High temperature hydrothermal potassic systems, metamorphic or igneous 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
511.886 154.320 (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. -4782450 (Ref.: Internal calculation) -5130970 (Ref.: 92cir/nav) Circone S. and Navrotsky A., 1992. Substitution of (6,4)Al in phlogopite : high pressure solution calorimetry , heat capacities and thermodynamic properties of the phlogopite -eastonite join. American Mineralogist, 77, p. 1191-1205. 424.020 (Ref.: 95dac/ben) Dachs, E. and Benisek, A., 1995. The stability of annite+quartz: reversed experimental data for the reaction 2 annite+3 quartz=2 sanidine+3 fayalite+2 H2O. Contributions to Mineralogy and Petrology, 121, p. 380-387. 389.87 (Ref.: 95dac/ben) Dachs, E. and Benisek, A., 1995. The stability of annite+quartz: reversed experimental data for the reaction 2 annite+3 quartz=2 sanidine+3 fayalite+2 H2O. Contributions to Mineralogy and Petrology, 121, p. 380-387.
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.
432.31 187.44 -87.40 (Ref.: 95dac/ben) Dachs, E. and Benisek, A., 1995. The stability of annite+quartz: reversed experimental data for the reaction 2 annite+3 quartz=2 sanidine+3 fayalite+2 H2O. Contributions to Mineralogy and Petrology, 121, p. 380-387.
Reaction properties

Annite + 10H+ ⇌ Al+3 + 3Fe+2 + K+ + 3H4SiO4

298.15 K, 1 bar log10K: 32.77 ΔH°r:-306153 J·mol-1 (Ref.: 92cir/nav) Circone S. and Navrotsky A., 1992. Substitution of (6,4)Al in phlogopite : high pressure solution calorimetry , heat capacities and thermodynamic properties of the phlogopite -eastonite join. American Mineralogist, 77, p. 1191-1205.
T(°C) 0 25 60 100 150 200 250 300
log10K 37.55 32.77 27.06 21.76 16.48 12.17 8.41 4.88
log10K(T) = A + B·T + C·T-1 + D·log10(T) + E·T−2 (T in Kelvin)
A B C D E
-2638.255782 -0.374606 166214.774871 941.114325 -9200205.801113