Identification of Biogenic Minerals from Different Origins by Infrared and Raman Spectroscopy, Including Low-Frequency Region

In fifteen words or less, explain the significance of this contribution (Novel Aspect).: New approach for analysis of biogenic minerals using IR and Raman spectroscopies including low-frequency region

Abstract Text:

Infrared (IR) and Raman spectroscopies are widely and complementarily used for identifying samples based on molecular vibration information. These techniques are also applicable to the low-frequency region and have been utilized in the analysis of crystal polymorphism in pharmaceuticals and the crystalline state of inorganic substances.

However, there have been few studies in which such composite analysis using IR and Raman spectroscopies has been applied to natural rocks or biogenic minerals such as shellfish in the past. Therefore, we focused on this unexplored area and analyzed natural rocks such as obsidian, as well as biogenic minerals such as shellfish composed of calcium carbonate, using attenuated total reflection mid- and far-infrared spectroscopy (ATR-IR and ATR-FIR, 4000-50 cm^-1) and Raman spectroscopy, including the low-frequency region. In our study, we demonstrated that ATR-FIR and Raman spectroscopies are highly effective for exploring polymorphism and differences in the crystal structure among aragonite biogenic minerals. In addition, we observed Boson peaks in the ultra-low-frequency region of the Raman spectra of obsidians (amorphous rocks) and found that the positions of Boson peaks varied depending on the formation ages and geological sources. In other words, we revealed that infrared (IR) and Raman spectroscopies, particularly in the case including the low-frequency region, are valuable tools for characterizing and identifying both crystalline materials such natural or biogenic materials and amorphous substances such as volcanic rocks.

In order to further advance our research, we are currently analyzing shellfish of different species and growth environments using IR and Raman spectroscopies, including the low-frequency region. This topic is particularly important because the mislabeling of shellfish origins has become a social issue in Japan.
In this presentation, we will report that we analyzed multiple shellfish of different species and growing environments and highlight the spectral differences in the OH, CO₃ region, as well as in the lattice vibrations of their crystal structures, observed in both IR and Raman spectra, including the low-frequency region.