The Raman spectrum of kaolinite #9 at 21°C

Abstract

The Raman spectrum of kaolinite #9, a layer silicate of composition Al2Si2O5(OH)4 from Mesa Alta, New Mexico, USA, is reported and compared to previously published Raman and infrared spectra, as well as calculated lattice vibration frequencies, of other kaolinite samples. In the OH stretching region, a Raman band is observed at 3684 cm−1, a frequency which is generally unknown in infrared spectra of kaolinite. The two most likely origins of this band are (a) uncoupled inner-surface hydroxyl stretching, and (b) transverse/longitudinal splitting involving the 3695 cm−1 band, which occurs in both Raman and infrared spectra of kaolinite. The existing data do not conclusively show which of these explanations is correct. In the lattice vibration region, most of the observed Raman bands of kaolinite #9 have been tentatively assigned by comparison with published frequency calculations and existing assignments of infrared spectra of various kaolinites. The descriptions of many of the vibrational modes are approximate, partly because extensive mixing of vibrations makes a simple description of them impossible.