Near-Infrared Spectroscopy Study of Serpentine Minerals and Assignment of the OH Group

Three different kinds of serpentine mineral samples were investigated using Fourier transform near-infrared spectroscopy (FTNIR). The results show that there are obvious differences in the characteristic infrared spectra of the three serpentine group minerals (lizardite, chrysotile, and antigorite), which can easily be used to identify these serpentine minerals. The combination of weak and strong peaks in the spectrum of lizardite appears at 3650 and 3690 cm⁻¹, while the intensities of the peaks at 4281 and 4301 cm⁻¹ (at 7233 and 7241 cm⁻¹, respectively) are similar. A combination of weak and strong peaks in chrysotile appears at 3648 and 3689 cm⁻¹ and at 4279 and 4302 cm⁻¹, and a single strong peak appears at 7233 cm⁻¹. In antigorite, there are strong single peaks at 3674, 4301, and 7231 cm⁻¹, and the remaining peaks are shoulder peaks or are not obvious. The structural OH mainly appears as characteristic peaks in four regions, 500–720, 3600–3750, 4000–4600, and 7000–7600 cm⁻¹, corresponding to the OH bending vibration, the OH stretching vibration, the OH secondary combination vibration, and the OH overtone vibration, respectively. In the combined frequency vibration region, the characteristic peak near 4300 cm⁻¹ is formed by the combination of the internal and external stretching vibrations and bending vibrations of the structural OH group. The overtone vibrations of the OH stretching vibration appear near 7200 cm⁻¹, and the practical factor is about 1.965. The near-infrared spectra of serpentine minerals are closely related to their structural differences and isomorphous substitutions. Therefore, near-infrared spectroscopy can be used to identify serpentine species and provides a basis for studies on the genesis and metallogenic environment of these minerals.