Paragonite

Formula : NaAl2(AlSi3)O10(OH)2

Space group: 
Monoclinic Space Group: C 2/c,Cc
Dana class: 
71.2.2a.2 (71) Phyllosilicate Sheets of Six-Membered Rings(71.2)with 2:1 Layers(71.2.2a) Mica Group (Muscovite subgroup)
High temperature: 
The stability range of paragonite is very large from 260C C in hydrothemal systems up to 750C with the pressure increase. The chemistry of the sediments plays a role on the stability of this mineral.
Geological context: 
Uncommon, but may be in large amounts, in low- to medium-grade metamorphic schists and phyllites, in muscovite-biotite gneisses, quartz veins, fine-grained sediments, and glaucophane-bearing rocks. It is also present as alteration of primary minerals in hydrothermal halo.

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
382.200 132.530 (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. -5556726 (Ref.: Internal calculation) -5937500 (Ref.: 96rou/hov) Roux J. and Hovis G. L., 1996. Thermodynamic mixing models for muscovite-paragonite solutions based on solution calorimetric and phase equilibrium data. Journal of Petrology, 37, p. 1241-1254 277.100 (Ref.: 84rob/hem) Robie R. A. and Hemingway B. S., 1984. Heat capacities and entropies of phlogopite KMg3AlSi3O1O(OH)2 and paragonite NaAl2AlSi3O1O(OH)2 between 5 and 9OO K and estimates of the enthalpies and Gibbs free energies of formation. Amer. Miner., 69, p. 858-868. 320.79 (Ref.: 84rob/hem) Robie R. A. and Hemingway B. S., 1984. Heat capacities and entropies of phlogopite KMg3AlSi3O1O(OH)2 and paragonite NaAl2AlSi3O1O(OH)2 between 5 and 9OO K and estimates of the enthalpies and Gibbs free energies of formation. Amer. Miner., 69, p. 858-868.
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.
349.98 200.51 -79.09 (Ref.: 84rob/hem) Robie R. A. and Hemingway B. S., 1984. Heat capacities and entropies of phlogopite KMg3AlSi3O1O(OH)2 and paragonite NaAl2AlSi3O1O(OH)2 between 5 and 9OO K and estimates of the enthalpies and Gibbs free energies of formation. Amer. Miner., 69, p. 858-868.
Reaction properties

Paragonite + 10H+ ⇌ 3Al+3 + Na+ + 3H4SiO4

298.15 K, 1 bar log10K: 16.80 ΔH°r:-294623 J·mol-1 (Ref.: 96rou/hov) Roux J. and Hovis G. L., 1996. Thermodynamic mixing models for muscovite-paragonite solutions based on solution calorimetric and phase equilibrium data. Journal of Petrology, 37, p. 1241-1254
T(°C) 0 25 60 100 150 200 250 300
log10K 21.39 16.80 11.28 6.12 0.91 -3.42 -7.27 -10.93
log10K(T) = A + B·T + C·T-1 + D·log10(T) + E·T−2 (T in Kelvin)
A B C D E
-2645.255861 -0.382473 164246.003967 940.700115 -9110764.074730