Raman spectroscopic study of the antimony bearing mineral langbanite

Raman spectroscopy has been used to characterise the antimonate mineral langbanite (Mn, Ca, Fe)(4)(2+)(Mn(3+), Fe(3+))(9)Sb(5+)Si(2)O(24). The mineral is characterised by a series of peaks in the 850-1200 cm(-1) region. Raman bands observed at 872 and 897cm(-1) are assigned to SbO antisymmetric and symmetric stretching vibrations, respectively. Associated with the SbO units are the bands at 330, 351 and 386 cm(-1) attributed to OSbO bending modes. Four Raman bands observed at 964, 986, 1012 and 1034 cm(-1) are assigned to SiO stretching vibrations. The observation of multiple SiO Raman bands provides evidence for the non-equivalence of the SiO units in the langbanite structure. Associated with the SiO units are the Raman bands at 542, 558, 646 and 671 cm(-1) attributed to OSiO bending modes. Low intensity bands are observed at 1130, 1200, 1432, 1718 and 1947 cm(-1) and are probably associated with delta SbOH deformation modes. Raman bands are observed at 3076 and 3476 cm(-1) and are assigned to strongly bonded water molecules involved in the langbanite structure. A sharp Raman band at 3680 cm(-1) are assigned to OH stretching vibrations. Raman spectroscopy provides evidence for water and OH units in the structure of langbanite and brings the formula of the mineral into question.