Quartz(alpha)

Formula : SiO2

Family: 
Oxides
Space group: 
Trigonal - Trapezohedral H-M Symbol (3 2) Space Group: P 3121,P 3221
Dana class: 
75.1.3.1 (75) Tectosilicate Si Tetrahedral Frameworks, (75.1)SiO2 with [4] coordinated Si(75.1.3) Dana Group
High temperature: 
At 1 bar pressure, the change from alpha-quartz to beta-quartz occurs very rapidly and reversibly at 573C.
Geological context: 
Occurs in hydrothermal veins, epithermal to alpine; characteristic of granites and granite pegmatites; in sandstones and quartzites, less abundant in other rock types; in hydrothermalmetal deposits.The alpha- and beta-forms of quartz (and tridymite and cristobalite) are special polymorph pairs, because their structures have all the same bonds (they're topologically identical) but the atoms are in shifted positions (they are geometrically distinct).

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 22.690 (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. -856281 (Ref.: Internal calculation) -910700 (Ref.: 82ric/bot) Richet P., Bottinga Y., Denielon L., Petitet J.P., and Tequi C., 1982. Thermodynamics properties of quartz, cristobalite and amorphous SiO2: Drop calorimetry measurements between 1000 and 1800 K and a review from 0 to 2000 K. Geochimica et Cosmochimica Acta, 46, p. 2639-2658. 41.439 (Ref.: 82ric/bot) Richet P., Bottinga Y., Denielon L., Petitet J.P., and Tequi C., 1982. Thermodynamics properties of quartz, cristobalite and amorphous SiO2: Drop calorimetry measurements between 1000 and 1800 K and a review from 0 to 2000 K. Geochimica et Cosmochimica Acta, 46, p. 2639-2658. 44.59 (Ref.: 82ric/bot) Richet P., Bottinga Y., Denielon L., Petitet J.P., and Tequi C., 1982. Thermodynamics properties of quartz, cristobalite and amorphous SiO2: Drop calorimetry measurements between 1000 and 1800 K and a review from 0 to 2000 K. Geochimica et Cosmochimica Acta, 46, p. 2639-2658.
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.
39.62 44.78 -7.45 (Ref.: 82ric/bot) Richet P., Bottinga Y., Denielon L., Petitet J.P., and Tequi C., 1982. Thermodynamics properties of quartz, cristobalite and amorphous SiO2: Drop calorimetry measurements between 1000 and 1800 K and a review from 0 to 2000 K. Geochimica et Cosmochimica Acta, 46, p. 2639-2658.
Reaction properties

Quartz(alpha) + 2H2O ⇌ H4SiO4

298.15 K, 1 bar log10K: -3.73 ΔH°r:23499 J·mol-1 (Ref.: 82ric/bot) Richet P., Bottinga Y., Denielon L., Petitet J.P., and Tequi C., 1982. Thermodynamics properties of quartz, cristobalite and amorphous SiO2: Drop calorimetry measurements between 1000 and 1800 K and a review from 0 to 2000 K. Geochimica et Cosmochimica Acta, 46, p. 2639-2658.
T(°C) 0 25 60 100 150 200 250 300
log10K -4.15 -3.73 -3.33 -2.99 -2.66 -2.39 -2.18 -2.01
log10K(T) = A + B·T + C·T-1 + D·log10(T) + E·T−2 (T in Kelvin)
A B C D E
-353.749111 -0.041888 21804.100389 124.192868 -1594286.171490