Phase relations of the nepheline-kalsilite system: X-ray diffraction and Mössbauer spectroscopy

The crystalline solutions in the nepheline-kalsilite (NaAlSiO4-KAlSiO4) system form an important group rock-forming tectosilicates, which have significant applications for materials science and implications for the geology field. The present studies on phase relations of the Fe-free and Fe-bearing nepheline-kalsilite systems have demonstrated that 10 mol % of Fe3+ substitution in Al3+ does not affect the phase relations of the solid solutions but causes the increase of lattice parameters. Analysis of the Mössbauer spectra has indicated that low-temperature carnegieite, low-temperature nepheline, and orthorhombic KAlSiO4 O1 phases in the Na(Al0.9Fe0.1)SiO4-K(Al0.9Fe0.1)SiO4 system only have one doublet assigned to high-spin Fe3+ with tetrahedral coordination, which means the doped Fe3+ cations occupy the Al3+ sites forming tetrahedrons with surrounding oxygen atoms based on charge balance.