The Anglesite spectrum is characterised by the same ν₁ band at 978 cm^-1. The rest of the vibrational modes have been found at frequencies of 450 cm^-1 and 553 cm^-1 for ν₂; 1058 cm^-1 and 1157 cm^-1 for ν₃; and for ν₄ - 611 cm^-1 and 646 cm^-1. These values are similar to those reported in the literature.

The peak corresponding to the symmetric stretching mode (ν₁) of the S-O bond in the sulfates appears to be the strongest in the Raman scattering intensity. The wavenumber of a Raman shift is determined by the bond strength and the atomic masses (Fadini and Schnepel, 1989). Therefore, the ν₁ wavenumber is a function of S-O stretching force constant in sulfates and increases with an increase in the force constant. The force constant of SO₄ tetrahedra were calculated from the bond lengths and the infrared absorption frequencies by Miyake et al. (1978).

Figure 1. Wavenumber of the ν1 vibrational Raman mode vs. atomic mass of the cations for barite group.

The stretching force constants are: for barite K = 6,27 md/Å; for celestine K = 6.34 md/Å; and for anglesite K = 5.98 md/Å. Therefore, this systematic wavenumber shift is largely due to the increase of mean force constants because of substitution of larger cations in the M sites (Lee et al., 2005). Also, the wavenumber decreases with an increase of the atomic mass of the cations. An example for ν1 mode is presented in figure 1, where the atomic masses are: Sr = 87.62 u; Ba = 137.32 u; Pb = 207.2 u.

• The Mineralogy Database [link]

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

• ¹BUZGAR N., BUZATU A., SANISLAV I. V. (2009) - The Raman study on certain sulfates. Analele Stiintifice ale Universitatii “Al. I. Cuza” - Iasi, Tome 55, issue 1, 5-23 [link]

• Beny, C. (1991) - Société Française de Minéralogie et de Cristallographie - Base de données de spectres Raman. Anglesite. [link]

• Fadini, A., Schnepel, F. M. (1989) - Vibrational spectroscopy methods and applications. Ellis Horwood Limited.

• Miyake, M., Minato, I., Morikawa, H., Iwai, S. (1978) - Crystal structures and sulphate force constants of barite, celestite and anglesite. American Mineralogist, 63, 506–510. [link]