Marialite (Na3Al3Si9O24·NaCl), the chloride end-member of the scapolite mineral group, is important for determining the chloride content of a paleofluid from which Cl-bearing scapolite formed as well as its potential role in the geochemical cycling of chlorine in tectonically active zones. Experiments on the upper-pressure stability of synthetic marialite breaking down to jadeite + coesite + halite at high pressures were done using a multi-anvil press in the range of 2. 6–4. 0 GPa and 1050–1250 °C for durations of 1–48 h. The boundary of this reaction was located along a straight line running from 2. 8 GPa and 1050 °C to 3. 5 GPa and 1250 °C. These data were then combined with data on the lower-thermal stability of marialite from this study and from previous work, along with published thermophysical data on synthetic marialite, to derive thermodynamic data for end-member marialite. The resultant 298 K and 1 atm value for the enthalpy of formation (H₅^o) is -12, 164. 03 ± 4. 7 kJ/mol and for the third-law entropy (S°) is 760. 34 ± 3. 8 J/K·mol for a volume of 329. 47 cm3/mol. These values provide good fits to the experimental data. The relatively high-temperature, high-pressure, and extremely high-salinity conditions needed to form end-member marialite means that albitite, rather than marialite, will tend to form at near-surface hydrothermal conditions. Scapolite is stabilized to typical intermediate-grade metamorphic conditions because of substantial solid solution of marialite with other scapolite components (i. e. , meionite and silvialite). Thermochemical data presented here can be used to determine the NaCl content of the paleobrine that formed Cl-bearing scapolite in, for example, the Dana Hill metagabbro of the northwest Adirondack Mountains, New York, which was found to be in the range of 32–56 wt% NaCl equivalent.
Kerstanski et al. (Sat,) studied this question.