A Raman spectroscopic study of humite minerals

Raman spectroscopy has been used to study the structure of the humite mineral group ((A(2)SiO(4))(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 A(2+) 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 (c) 2006 John Wiley & Sons, Ltd.