Vibration spectra and new structural data on natural layered silicate-phosphate harrisonite from various geological environments.

Raman and FTIR spectroscopy are widely used methods for research of crystalline compounds and their structural properties. Limited vibration spectroscopic data are available on silicate-phosphate phases. We provide fully deconvoluted and characterized Raman and FTIR spectra of chemically and structurally well-defined natural crystalline silicate-phosphate harrisonite from different geological environments. All fundamental silicate and phosphate vibration modes are identified and discussed. The interpretation of harrisonite spectra is supported by theoretical normal vibration mode calculations. The absence of hydrogen in the structure of harrisonite was confirmed using vibration spectroscopy. The identification of phases using Raman and FTIR spectroscopy relies on existence of reliable and high-quality reference spectra. The vibrational spectra of harrisonites with different chemical compositions are similar with each other and distinct from spectra of other minerals. All published records of harrisonite were revised, and the available material from various geological environments was thoroughly characterized using both chemical (EMPA) and structural (SC-XRD) methods.