Characterization and Identification of Biogenic Minerals from Different Growing Environments Using Infrared and Raman Spectroscopies Including Low-Frequency Regions

Attenuated total reflection infrared-far-infrared (ATR IR-FIR) spectra (4000-50 cm^-1) and Raman spectra (2000-50 cm^-1) were measured for twelve types of biogenic minerals (shells), including <i>Corbicula sandai</i> (aragonite), <i>Corbicula fluminea</i> (aragonite), <i>Corbicula japonica</i> (aragonite), <i>Ruditapes philippinarum</i> (aragonite), and <i>Mytilus galloprovincialis</i> (aragonite and calcite) from different origins and growing environments. In this study, we investigated the crystal structures of these biogenic minerals, the water contents and structure in them, and the differences in the crystal structures among the aragonite forms of these minerals. In the 4000-3000 cm^-1 region and around the 1650 cm^-1 band region in the IR spectra, the proportion of the IR absorption bands related to weak and strong hydrogen bonds was significantly different among the shellfish species investigated. Therefore, it has been found that IR spectroscopy is useful for discriminating among shells based on the content and structure of water such as hydrogen bonds. In the low-frequency region below 500 cm^-1, where bands corresponding to lattice vibrational modes are observed, we investigated the lattice vibration modes of aragonite of shells and discussed particularly the full width at half-maximum (FWHM) of the bands at around 267 cm^-1 in the FIR spectra and the intensity of the side band at around 140 cm^-1 in the Raman spectra. As a result, we demonstrated that using both IR and Raman spectroscopies including the low-frequency regions allows us to distinguish various biogenic minerals from different habitats and growing environments. Additionally, it suggests that both IR and Raman spectroscopies including low-frequency regions are useful for characterizing habitats of shellfish.