A vibrational spectroscopic study of the silicate mineral normandite--NaCa(Mn(2+),Fe(2+))(Ti,Nb,Zr)Si2O7(O,F)2.

We have studied the mineral normandite using a combination of scanning electron microscopy with energy dispersive spectroscopy and vibrational spectroscopy. The mineral normandite NaCa(Mn(2+),Fe(2+))(Ti,Nb,Zr)Si2O7(O,F)2 is a crystalline sodium calcium silicate which contains rare earth elements. Chemical analysis shows the mineral contains a range of elements including Na, Mn(2+), Ca, Fe(2+) and the rare earth element niobium. No Raman bands are observed above 1100 cm(-1). The mineral is characterised by Raman bands observed at 724, 748, 782 and 813 cm(-1). Infrared bands are broad; nevertheless bands may be resolved at 723, 860, 910, 958, 933, 1057 and 1073 cm(-1). Intense Raman bands at 454, 477 and 513 cm(-1) are attributed to OSiO bending modes. No Raman bands are observed in the hydroxyl stretching region, but low intensity infrared bands are observed at 3191 and 3450 cm(-1). This observation brings into question the true formula of the mineral.