Frankamenite: Relationship between the Crystal–Chemical and Vibrational Properties

Abstract

The study provides novel insights into the crystal–chemical and optical characteristics of frankamenite. Frankamenite belongs to a special group (canasite group) of the complex alkaline Ca-(K)-(Na) silicates, and it was found in charoitites from the only known location, Murun Massif, Eastern Siberia, Russia. The crystal–chemical, vibrational, and optical properties of frankamenite were investigated by combining electron probe microanalysis (EPMA), single-crystal X-ray diffraction (SCXRD), infrared (IR) absorption, Raman, UV-Visible absorption, and electron spin resonance (ESR) spectroscopy. The behavior of the peaks in the IR spectra was also studied using ab initio calculations. Detailed characteristics of the internal composition and structure of the mineral species were described, and vibrational and optical properties based on these peculiarities were interpreted. The thermally stimulated reorientation of the H2O molecules and OH− groups was studied by thermo-Raman spectroscopy. Octahedral cationic positions can be readily doped with transition metal and lanthanide ions that provide a promising opportunity to adjust the Ce3+ luminescence. Hence, frankamenite is a potential material for ion exchange, novel phosphors, and luminophores.