Sanidine

Formula : K(AlSi3)O8

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 11.06.2018

THERMODYNAMICS

Individual properties (298.15 K)
M
g·mol-1
cm3·mol-1
ΔGºf
J·mol-1
ΔHºf
J·mol-1
J·mol-1·k-1
CP
J·mol-1·K-1
278.332 109.008 -3745958 -3965730 232.900 204.55
Reaction properties

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

298.15 K, 1 bar log10K: 0.58 ΔH°r: -65073 J·mol-1
T(°C) 0 25 60 100 150 200 250 300
log10K 1.62 0.58 -0.62 -1.71 -2.83 -3.78 -4.69 -5.61