A vibrational spectroscopic study of the silicate mineral inesite Ca2(Mn,Fe)7Si10O28(OH)•5H2O

We have studied the hydrated hydroxyl silicate mineral inesite of formula Ca-2(Mn,Fe)(7)Si10O28(OH)center dot 5H(2)O using a combination of scanning electron microscopy with EDX and Raman and infrared spectroscopy. SEM analysis shows the mineral to be a pure monomineral with no impurities. Semiquantitative analysis shows a homogeneous phase, composed by Ca, Mn2+, Si and P. with minor amounts of Mg and Fe. Raman spectrum shows well resolved component bands at 997, 1031, 1051, and 1067 cm(-1) attributed to a range of SiO symmetric stretching vibrations of [Si10O28] units. Infrared bands found at 896, 928, 959 and 985 cm(-1) are attributed to the OSiO antisymmetric stretching vibrations. An intense broad band at 653 cm(-1) with shoulder bands at 608, 631 and 684 cm(-1) are associated with the bending modes of the OSiO units of the 6- and 8-membered rings of the [Si10O28] units. The sharp band at 3642 cm(-1) with shoulder bands at 3612 and 3662 cm(-1) are assigned to the OH stretching vibrations of the hydroxyl units. The broad Raman band at 3420 cm(-1) with shoulder bands at 3362 and 3496 cm(-1) are assigned to the water stretching vibrations. The application of vibrational spectroscopy has enabled an assessment of the molecular structure of inesite to be undertaken. (C) 2014 Elsevier B.V. All rights reserved.