Sanidine

Formula : K(AlSi3)O8

Family: 
Feldspar
Space group: 
Monoclinic - Prismatic H-M Symbol (2/m) Space Group: C 2/m
Dana class: 
76.1.1.2 (76) Tectosilicate Al-Si Framework (76.1) with Al-Si frameworks (76.1.1)K (Na,Ba) feldspars
High temperature: 
The stability of this mineral depends on substitution (fluorine) and pressure, the stability domain ranges between around 400C to 1600C
Geological context: 
High sanidine forms a series with high albite. Most common in felsic volcanic and hypabyssal rocks as rhyolites, phonolites, trachytes; as spherulites in volcanic glass. Also from ultrapotassic mafic, high-temperature contact metamorphic (sanidinite facies), and hydrothermally altered rocks. From eclogite nodules in kimberlite.

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
278.332 109.008 (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. -3745798 (Ref.: Internal calculation) -3965600 (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. 232.800 (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. 204.55 (Ref.: 06bla/pia) Blanc P., Piantone P., Lassin A. et Burnol A., 2006. Thermochimie : Selection de constantes thermodynamiques pour les elements majeurs, le plomb et le cadmium. Rapport final. Rapport BRGM 54902-FR
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.
206.22 142.00 -39.12 (Ref.: 06bla/pia) Blanc P., Piantone P., Lassin A. et Burnol A., 2006. Thermochimie : Selection de constantes thermodynamiques pour les elements majeurs, le plomb et le cadmium. Rapport final. Rapport BRGM 54902-FR
Reaction properties

Sanidine + 4H+ + 4H2O ⇌ Al+3 + K+ + 3H4SiO4

298.15 K, 1 bar log10K: 0.62 ΔH°r:-58203 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 1.42 0.62 -0.54 -1.70 -2.91 -3.93 -4.88 -5.85
log10K(T) = A + B·T + C·T-1 + D·log10(T) + E·T−2 (T in Kelvin)
A B C D E
-1604.077645 -0.213689 99754.211519 567.690110 -6300812.597593