Coesite(alpha)

Formula : SiO2

Family: 
Space group: 
Monoclinic - Prismatic H-M Symbol (2/m) Space Group: C 2/c
Dana class: 
75.1.4.1 (75) Tectosilicate Si Tetrahedral Frameworks(75.1) SiO2 with [4] coordinated Si (75.1.4) Dana Group
High temperature: 
Coesite is a high presure mineral its stability is limited by stishovite (an other silica polymorph) at about 65 kbar.
Geological context: 
Formed at pressures in excess of 20 kbar, as fine-grained intergrowths with quartz and silica glass in impact metamorphosed rocks and tektites. A primary phase in grospydite (kyanite-garnet-clinopyroxene) xenoliths in kimberlite, and intergrown with quartz as inclusions in garnet and clinopyroxene within eclogites of high-grade metamorphic terranes.

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
60.084 20.641 -851577 -906313 40.376 43.54
Reaction properties

Coesite(alpha) + 2H2O ⇌ H4SiO4

298.15 K, 1 bar log10K: -2.92 ΔH°r: 16779 J·mol-1
T(°C) 0 25 60 100 150 200 250 300
log10K -3.18 -2.92 -2.60 -2.31 -2.02 -1.79 -1.61 -1.47