Cristobalite(alpha)

Formula : SiO2

Family: 
Oxides
Space group: 
Tetragonal - Trapezohedral H-M Symbol (4 2 2) Space Group: P 41212
Dana class: 
75.1.1.1 (75) Tectosilicate Si Tetrahedral Frameworks (75.1)SiO2 with [4] coordinated Si (75.1.1) Dana Group
High temperature: 
Above approximately 1470C to the melting point of silica round 1713C.Alpha cristobalite undergoes a first phase transition at 200C-275C, from cubic to tetragonal phase beta cristobalite.
Geological context: 
Present in volcanic rocks, it form from molten rock at temperatures above approximately 1470 degrees Celsius to the melting point of silica (around 1713C)

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
60.084 25.740 (Ref.: 04fab/sax) Fabrichnaya O., Saxena S.K., Richet P. and Westrum E.F. (Eds), 2004. Thermodynamic data, models, and phase diagrams in multicomponent oxide systems. ISBN 3-540-14018-2 Springer Verlag Berlin Heidelberg New York, 198 p. -852989 (Ref.: Internal calculation) -906030 (Ref.: 04fab/sax) Fabrichnaya O., Saxena S.K., Richet P. and Westrum E.F. (Eds), 2004. Thermodynamic data, models, and phase diagrams in multicomponent oxide systems. ISBN 3-540-14018-2 Springer Verlag Berlin Heidelberg New York, 198 p. 46.060 (Ref.: 04fab/sax) Fabrichnaya O., Saxena S.K., Richet P. and Westrum E.F. (Eds), 2004. Thermodynamic data, models, and phase diagrams in multicomponent oxide systems. ISBN 3-540-14018-2 Springer Verlag Berlin Heidelberg New York, 198 p. 44.32 (Ref.: 04fab/sax) Fabrichnaya O., Saxena S.K., Richet P. and Westrum E.F. (Eds), 2004. Thermodynamic data, models, and phase diagrams in multicomponent oxide systems. ISBN 3-540-14018-2 Springer Verlag Berlin Heidelberg New York, 198 p.
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.
33.47 49.28 -3.42 (Ref.: 04fab/sax) Fabrichnaya O., Saxena S.K., Richet P. and Westrum E.F. (Eds), 2004. Thermodynamic data, models, and phase diagrams in multicomponent oxide systems. ISBN 3-540-14018-2 Springer Verlag Berlin Heidelberg New York, 198 p.
Reaction properties

Cristobalite(alpha) + 2H2O ⇌ H4SiO4

298.15 K, 1 bar log10K: -3.16 ΔH°r:18829 J·mol-1 (Ref.: 04fab/sax) Fabrichnaya O., Saxena S.K., Richet P. and Westrum E.F. (Eds), 2004. Thermodynamic data, models, and phase diagrams in multicomponent oxide systems. ISBN 3-540-14018-2 Springer Verlag Berlin Heidelberg New York, 198 p.
T(°C) 0 25 60 100 150 200 250 300
log10K -3.50 -3.16 -2.84 -2.57 -2.32 -2.11 -1.94 -1.81
log10K(T) = A + B·T + C·T-1 + D·log10(T) + E·T−2 (T in Kelvin)
A B C D E
-354.401695 -0.041703 22114.271137 124.273566 -1600147.200706