A comparison between the Raman spectra of the pargasite samples (3-1, 3-2 and 3-2) and one reference sample of pargasite from the RRUFF project (R060632) is illustrated in figure 8 (see reference paper¹). As has been discussed in the Analytical procedure section, some spectra are raw for a better interpretation, and these particular spectra are some of them. Also, the Raman spectra of these samples were very difficult to obtain. The below table summarizes the entire discussion about the assignments of the peaks.

The ν_s (ν₁) of the Si-O_b-Si lies at 663, 667, 663 and 665 cm^-1 (for 3-1; 3-2; 3-2 and R060632, respectively). In our spectra, a very broad band exhibits at 758-766 cm^-1, while in the case of R060632 two bands appear at 750 and 801 cm^-1. If we look carefully at the highest peak (assigned to ν₁), on the right it exhibits a one shoulder band (around 692-695 cm^-1), which appears in all spectra of pargasite and may be due to 2Al in the T site. The high intensity of the band at ~760 cm^-1 can also be explained by 2Al in the T site or the orientation of the laser beam on the pargasite samples.

The interpretation of the spectra in the 850-1200 cm^-1 is generally based on the bands dominantly arising from the vibrations of symmetric stretching and asymmetric stretching (Si₄O₁₁), as follows: the bands between 885 and 928 cm^-1 may be ascribed to the symmetric stretching (ν_s) of the O-Si-O linkage; the peaks observed in the 950-1000 cm^-1 region are attributed to the asymmetric stretching (ν_as) of the O-Si-O linkage. The highest-frequency bands, observed in 1000-1100 cm^-1 spectral region, may be ascribed to the asymmetric stretching vibration of the Si-O_b-Si bridges.

All three spectra of pargasite samples (3-1 and 3-2; 3-2) present one peak at ~2330 cm^-1, which may be assigned to H₃O⁺ vibrations; the appearance of this band is due to the substitution of K or Na with H₃O⁺ (K, Na - H₃O⁺).

• The Mineralogy Database [link]

• Crystal data (.cif file) from the American Mineralogist Crystal Structure Database [link]

• ¹APOPEI A. I., BUZGAR N. (2010) - The Raman study of amphiboles. Anal. Şt. Univ. “Al. I. Cuza” Iaşi, Geologie, LVI/1 [link]

• Pargasite spectrum from the RRUFF project [link]

• Downs, R. T. 2006. The RRUFF Project: an integrated study of the chemistry, crystallography, Raman and infrared spectroscopy of minerals. Program and Abstracts of the 19th General Meeting of the International Mineralogical Association in Kobe, Japan. O03-13.

• Huang, E. (2003) - Raman Spectroscopic Study of Amphiboles. PhD thesis in Chinese.