Fig. 2: Unpolarised FTIR spectra of omphacite (Obn112 sample).

In the Fourier Transform Infra Red (FTIR) spectra, the 2800–5500 cm⁻¹ range show main peaks in the 3000–3800 cm⁻¹ range corresponding to OH and molecular H₂O (stretching). Secondary peaks in the 3800–6000 cm⁻¹ interval correspond to molecular H₂ (4100 cm⁻¹), Si-OH (4470 cm⁻¹), and molecular water (5200 cm⁻¹). A comparison between unheated and heated samples (500 and 600 °C) shows decreasing intensity of the peak at 4100 cm⁻¹ with increasing temperature. The widening of the peak with increasing H₂ content is due to overlapping with two smaller peaks at 4200 and 3950 cm⁻¹. Note that the low intensity of the band at 5200 cm⁻¹ related to molecular water indicates negligible fluid inclusion contributions.