For clinopyroxenes, the group theory predicts 30 Raman modes: 14A_g + 16B_g (Rustein and White, 1971).

The spectra of diopside and hedenbergite (see reference paper¹ or above spectrum for hedenbergite) are also characterized by two intense bands, corresponding to the Si-O_nbr stretching mode (1010 cm^-1 in diopside and 1012 cm^-1 in hedenbergite) and to the stretching of Si-O_br bonds (665 cm^-1 in diopside and 663 cm^-1 in hedenbergite). In the 500-560 cm^-1 region, bands assigned to the O-Si-O bending modes were observed, and in the lower region, bands attributed to the cation-oxygen vibrations (see below table).

Huang et al. (2000) showed that with a constant Ca content most Raman bands in diopside-hedenbergite series should decrease with an increase of the Fe concentration. In all spectra from the present study, this observation is available only for the bands located in the 200-800 cm^-1 region and for the peak from ~1040 cm^-1; the ~850 cm^-1 band preserves the same position, and the band at ~1010 cm^-1 is slightly higher in hedenbergite (1010 cm^-1 in diopside samples and 1012 cm^-1 in hedenbergite sample 5799). The Raman spectra of diopside are similar to those reported in the literature (Etchepare, 1971; Swamy et al., 1997; Huang et al., 2000). The spectra of hedenbergite are different from those reported by Huang et al. (2000) (see above table), especially for the low region attributed to the cation-oxygen vibration modes. These differences are probably caused by a higher content of Mg in M1 sites in our studied samples.

• The Mineralogy Database [link]

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

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

• Huang, E., Chen, C.H., Huang, T., Lin, E.H., Xu, J., (2000) - Raman spectroscopic characteristics of Mg-Fe-Ca pyroxenes. American Mineralogist, 85, 473–479.

• Rutstein, M.S., White, W.B., (1971) - Vibrational spectra of high-calcium pyroxenes and pyroxenoids. American Mineralogist, 56, 877–887.

• Etchepare, J., (1971) - Study by Raman spectroscopy of crystalline and glassy diopside. In: Douglas, R.W., Ellis, B. (Eds.), Amorphous materials. Wiley Interscience, London, 337–346.

• Swamy, V., Dubrovinsky, L.S., Matsui, M., (1997) - High-temperature Raman spectroscopy and quasi-harmonic lattice dynamic simulation of diopside. Phys. Chem. Minerals, 24, 440–446.