Raman spectroscopy of the mineral rhodonite

The mineral rhodonite an orthosilicate has been characterised by Raman spectroscopy. The Raman spectra of three rhodonites from Broken Hill, Pachapaqui and Franklin were compared and found to be similar. The spectra are characterised by an intense band at around 1000 cm−1 assigned to the ν1 symmetric stretching mode and three bands at 989, 974 and 936 cm−1 assigned to the ν3 antisymmetric stretching modes of the SiO4 units. An intense band at around 667 cm−1 was assigned to the ν4 bending mode and showed additional bands exhibiting loss of degeneracy of the SiO4 units. The low wave number region of rhodonite is complex. A strong band at 421.9 cm−1 is attributed to the ν2 bending mode. The spectra of the three rhodonite mineral samples are similar but subtle differences are observed. It is proposed that these differences depend upon the cationic substitution of Mn by Ca and/or Fe2+ and Mg.