The spodumene Raman spectrum is shown above. The Raman bands characteristic for pyroxenes appear at higher frequencies in the spodumene spectrum. The bands corresponding to the Si-O_nbr vibrations are observed at 1017 cm^-1, 1070 cm^-1 and 1098 cm^-1. The stretching modes of Si-O_br bonds are located at 705 cm^-1 and 783 cm^-1. The bands attributed to O-Si-O bending in calcium pyroxene correspond to 522 cm^-1 and 582 cm^-1 in spodumene. Sharma and Simons (1981) assigned the 522 cm^-1 band to the Al-O stretching mode of the AlO₆ group, together with 478 cm^-1 and 438 cm^-1. The other bands from the low region of the spectrum are assigned to the cation-oxygen interactions (see below table). A series of Raman studies were made on spudemene in order to follow the effects of phase transition from low (C2/c) to high (P21/c) pressure (Pommier et al., 2003).

In all studied clinopyroxenes with a C2/c structure, the Raman spectra have the same shape, showing bands of the characteristic vibrations: M-O modes, Si-O bending, Si-O_br stretching and Si-O_nbr stretching. The differences between minerals appear in the positions of these peaks. In the aegirine spectra the bands assigned to the Si-O stretch are observed at 544 cm^-1 and 953-971 cm^-1; in diopside, hdenbergite and augite, these bands appear at ~665 cm^-1 and ~1010 cm^-1, while in spodumene – at 705 cm^-1 and 1070 cm^-1. This shifting of the position of the bands from lower (aegirine) to medium (diopside, hedenbergite and augite) to higher frequencies (spodumene) appears to be related to the chemical composition in the M1 and M2 sites. The bands shift on higher wavenumbers with a decrease of the cation size in the M2 site, from Na⁺ to Ca²⁺ to Li⁺. The high strength of M2-O bonds restricts the motion of Si-O bonds, making them vibrate at higher wavenumbers.

• 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]

• Pommier, C.J.S., Downs, R.T., Stimpfl, M., Redhammer, G.J., Denton, M.B., (2005) - Raman and X-ray investigations of LiFeSi₂O₆ pyroxene under pressure. Journal of Raman Spectroscopy, 36, 864–871.

• Sharma, S.K., Simons, B., (1981) - Raman study of crystalline polymorphs and glasses of spodumene composition quenched from various pressures. American Mineralogist, 66, 118–126.