Chalcedony

Formula : SiO2

Family: 
Space group: 
Trigonal
High temperature: 
Very low temperature environments (amorphous)
Geological context: 
Stable in very low temperature environments, even sedimentary mineral. Traditionally defined as a fibrous cryptocrystalline variety of Quartz, more recently, it has been shown that much Chalcedony is a mixture of Quartz and Moganite, another Silica mineral.

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 22.688 -854659 -909108 41.338 44.47
Reaction properties

Chalcedony + 2H2O ⇌ H4SiO4

298.15 K, 1 bar log10K: -3.46 ΔH°r: 19574 J·mol-1
T(°C) 0 25 60 100 150 200 250 300
log10K -3.77 -3.46 -3.09 -2.75 -2.42 -2.16 -1.95 -1.78