Abstract

Phase relations in the system NaAlSiO4-NaGaSiO4 to 945° C at 1 kbar P(H2O) are dominated by stability of Na(Al,Ga)SiO4 with the beryllonite-type structure. The nepheline structure is restricted to NaAlSiO4-rich compositions at moderate and high temperature. Structure-composition relationships are controlled by space-fitting requirements of both framework and cavity cations, as in related systems. The two-phase (nepheline-type+beryllonite-type) field has been delineated from the end-member NaAlSiO4 composition up to the peritectic point at about 945° C (and 60 mol% NaGaSiO4), using a volume-composition relationship for the beryllonite-type phase, phase appearance, and electron microprobe analysis. At end-member NaGaSiO4 composition, the beryllonite-type phase is stable to the melting point (902±5° C). At end-member NaAlSiO4 composition, the beryllonite-type⇌nepheline-type transformation occurs at 348±2° C, and is associated with an increase in molar volume of 2.4% and enthalpy of 5170±40J·mol−1. Thus, end-member NaAlSiO4 nepheline, and probably all sub-potassic nephelines as well, are metastable at very-low geological temperatures.

Talk to us

Join us for a 30 min session where you can share your feedback and ask us any queries you have

Schedule a call

Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.