Electronic and vibrational spectra of Mn rich sursassite.

The optical spectrum of Mn2+ in octahedral coordination for sursassite is characterized by well resolved bands at 580, 515, 470, 390, 340, and 295 nm (17240, 19420, 21280, 25640, 29410 and 33900 cm-1). Crystal field parameters evaluated from the observed bands are Dq=690, B=680 and C=2800 cm-1. A broad band centred around 13000 cm-1 attributed to Fe(III) ion is an impurity in sursassite confirmed from EDX analysis. Vibrational spectra have been investigated both by IR and Raman spectroscopy. The correlation between vibrational modes and the structural properties of the manganese silicate, sursassite, is made and compared with other silicates. Two vibrational modes of CO(3)2- observed; the antisymmetric stretching mode (nu3) at 1420 cm-1 (IR active) and the out-of-plane bending mode (nu2) (IR and Raman active) at approximately 875 cm-1. This confirms the Mn rich phases in sursassite as observed from SEM probably an Mn carbonate-rhodochrosite.