Prior to any discussions about the Raman spectra of the grunerite samples, it should be noted that in some papers the term grunerite is replaced with amosite (the commercial name for grunerite).

For each grunerite spectrum, the peaks are listed below with all assignments. These spectra are very similar – the ν₁ (A_1g) symmetric stretching (ν_s) of the Si-O_b-Si bridge is shown in all spectra (fig. 4, see reference paper) around 660 cm^-1, more exactly at 665 cm^-1 for the grunerite samples of this work and at 663 cm^-1 and 661 cm^-1, respectively, for reference spectra (R070186 and R060062). In the 745-790 cm^-1 spectral region, three bands are shown in the grunerite sample, with the main band at 761 cm^-1 (the other two peaks are located at 747 cm^-1 and 785 cm^-1, respectively). These bands are assigned to the symmetric stretching (ν_s) of the O-Si-O linkage. Also, the 909 cm^-1 spectral band is assigned to the ν_s of the O-Si-O linkage (all of these bands assigned to the ν_s of the O-Si-O linkage have a low intensity).

The bands situated in the upper region of the 950 cm^-1 wavenumber (950-1200 cm^-1) are assigned to antisymmetric (or asymmetric) stretching vibration (ν_as). More specifically, the band at 971 cm^-1 may be assigned to the ν_as of the O-Si-O linkage. We consider that the peak at 999 cm^-1 is part of the 1027 cm^-1 vibration (due to the fact that, in the reference spectra of Bard et al. (1997) and Rinaudo et al. (2004), this peak is slightly overlapped), which, together with the peak at 1098 cm^-1, is assigned to ν_as Si-O_b-Si bridges. The overlapping of the 999 cm^-1 peak can be seen even in figure 4 (see reference paper) (in the case of R060062).

Below 625 cm^-1, the wavenumber exhibits three main bands and other bands that can be considered part of the main bands. As we have discussed in the Raman modes of amphiboles (see reference paper¹) part and according to Rinaudo et al. (2004), the bands between 210-300 cm^-1 are assigned to the O-H-O groups or, if we respect the assignments of Shurvell et al. (2001) and Huang (2003), this region may be ascribed to lattice vibration – both are questionable, but the second assignment is more plausible. Therefore, the peaks at 242 cm^-1 and 289 cm^-1 belong to the O-H-O group or the lattice mode. Not the same thing can be said about the peak at 315 cm^-1 (despite the first impression), because it is more of a part of M-O vibrations. However, this assignment (of the 315 cm^-1 peak) remains controversial if we look at the spectra compared with the 1-1 grunerite sample; another reason is the very low intensity.

If we take a look at the ideal chemical formula of grunerite (□Fe²⁺₇Si₈O₂₂(OH)₂), just Fe²⁺ is involved in the external vibrations (M²⁺-O); consequently, the bands situated at 363 cm^-1 and 415 cm^-1 may be ascribed to the Fe²⁺-O vibration mode.

The spectrum of grunerite also presents two bands at 533 cm^-1 and 566 cm^-1, respectively, which may be assigned to the deformation mode of the silicate chain. According to Kloprogge et al. (2001), the libration and translation modes of OH^- lie in the same spectral region, are probably overlapped or the very low intensity peak at 566 cm^-1 may be assigned to the librational or translational mode of the OH^- group – this assignment is, however, uncertain.

• 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]

• Grunerite 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.

• Bard, T., Yarwood, J., Tylee, B. (1997) - Asbestos fiber identification by Raman microspectroscopy. J. Raman Spectrosc., 28, 803-809

• Rinaudo, C., Belluso, E., Gastaldi, D. (2004) - Assessment of the use of Raman spectroscopy for the determination of amphibole asbestos. Mineralogical Magazine 68 (3): 443-453.

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

• Kloprogge, J. T., Visser, D., Ruan, H., Frost, R. L. (2001) - Infrared and Raman spectroscopy of holmquistite, Li₂(Mg,Fe²⁺)₃(Al,Fe³⁺)₂(Si,Al)₈O₂₂(OH)₂. Journal of Materials Science Letters, 20, 1497-1499.