High temperature solution calorimetry of synthetic quartz, coesite and stishovite provides enthalpies of transition. ΔH9750 for quartz-coesite and ΔH2980 for coesite-stishovite transition are 320 ± 70 and 11700 ± 410 cal mol-1, respectively. The present transformation enthalpy data represent a small but significant revision of those of Holm et al. Using the published phase equilibrium data, thermal expansivity, compressibility and heat capacity data, ΔS9750 for the quartz-coesite and ΔS2980 for the coesite-stishovite transition are -1.2 ± 0.1 and -1.0 ± 0.4 cal K-1 mol-1, respectively. These thermochemical data are used to calculate phase boundaries of the transitions. The calculated quartz-coesite transition boundary agrees well with the one determined experimentally by Bohlen and Boettcher. The calculated coesite-stishovite boundary is generally consistent with data by Yagi and Akimoto and by Suito.
ASJC Scopus subject areas
- Astronomy and Astrophysics
- Physics and Astronomy (miscellaneous)
- Space and Planetary Science