A Raman spectroscopic study of humite minerals

Abstract Raman spectroscopy has been used to study the structure of the humite mineral group ((A2SiO4)n–A(OH, F)2 where n represents the number of olivine and brucite layers in the structure and is 1, 2, 3 or 4 and A2+ is Mg, Mn, Fe or some mix of these cations). The humite group of minerals forms a morphotropic series with the minerals olivine and brucite. The members of the humite group contain layers of the olivine structure that alternate with layers of the brucite‐like sheets. The minerals are characterized by a complex set of bands in the 800–1000 cm−1 region attributed to the stretching vibrations of the olivine (SiO4)4− units. The number of bands in this region is influenced by the number of olivine layers. Characteristic bending modes of the (SiO4)4− units are observed in the 500–650 cm−1 region. The brucite sheets are characterized by the OH stretching vibrations in the 3475–3625 cm−1 wavenumber region. The position of the OH stretching vibrations is determined by the strength of the hydrogen bond formed between the brucite‐like OH units and the olivine silica layer. The number of olivine sheets and not the chemical composition determines the strength of the hydrogen bonds. Copyright © 2006 John Wiley & Sons, Ltd.