Pyrope(alpha)

Formula : Mg3Al2Si3O12

Family: 
Garnet
Space group: 
Isometric - Hexoctahedral H-M Symbol (4/m 3 2/m) Space Group: I a3d
Dana class: 
51.4.3a.1 (51) Nesosilicate Insular SiO4 Groups Only (51.4) with cations in [6] and >[6] coordination (51.4.3a) Garnet group (Pyralspite series)
High temperature: 
Stability of pyrope is above 650C.
Geological context: 
Occurs in high-grade metamorphic ultramafic rocks, as peridotites, kimberlites, eclogites, serpentinites, and in "hornblende"-garnet-plagioclase rocks and anorthosites. Also in amphibole and biotite schists.

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
403.127 113.270 (Ref.: 78hel/del,78rob/hem) -5932799 (Ref.: Internal calculation) -6285000 (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. 260.663 (Ref.: 78hel/del,78rob/hem) 325.88 (Ref.: 78hel/del,78rob/hem)
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.
383.63 136.57 -87.53 (Ref.: 78hel/del,78rob/hem)
Reaction properties

Pyrope(alpha) + 12H+ ⇌ 2Al+3 + 3Mg+2 + 3H4SiO4

298.15 K, 1 bar log10K: 58.93 ΔH°r:-569383 J·mol-1 (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.
T(°C) 0 25 60 100 150 200 250 300
log10K 67.92 58.93 48.36 38.63 28.94 21.07 14.34 8.22
log10K(T) = A + B·T + C·T-1 + D·log10(T) + E·T−2 (T in Kelvin)
A B C D E
-3163.219169 -0.456459 206534.845764 1125.786427 -10681752.229538