Structural characterization of rondorfite, calcium silica chlorine mineral containing magnesium in tetrahedral position [MgO4]6−, with the aid of the vibrational spectroscopies and fluorescence

Raman and infrared spectra of rondorfite Ca8Mg(SiO4)4Cl2, a calcium chlorosilica mineral containing magnesium in tetrahedral position, has been studied in terms of spectra-structure relations. Raman spectra have been measured at different excited laser lines: 780 nm, 532 nm, 488 nm and 457 nm. This mineral is characterized by a single sharp intense Raman band at 863 cm−1 assigned to the ν1 [SiO4]4− (Ag) symmetric stretching mode in the magnesiosilicate pentamer. Due to symmetry restriction the other Raman bands have a small intensity. Two Raman bands observed at 564 cm−1 and 526 cm−1 are associated simultaneously with ν4 [MgO4]6− and ν4 [SiO4]4− symmetric and antisymmetric modes where magnesium occurs in the tetrahedral configuration. The weak bands at 422 cm−1 and 386 cm−1 are associated with the ν2 bending mode of CaO6 in octahedral configuration, respectively. Moreover the infrared spectrum shows very weak bands associated with the hydroxyl group and/or water molecule. Additionally, the strong fluorescence phenomenon was observed and related to the presence of chlorine atoms, magnesium Mg2+ ions in atypical configuration or point defects.

Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Spectroscopic (infrared and Raman) analysis of the rare chlorosilicate mineral.► The localized bands derived from the vibration of Mg2+ in tetrahedral configuration.► Description of bands connected with the vibration of magnesiosilicate pentamer.► Study of the fluorescence at different excitation laser line.► Discussion of a new possibilities of application of the study mineral.