The Near-Infrared Combination Band Frequencies of Dioctahedral Smectites, Micas, and Illites

James L. Post and Paul N. Noble
Department of Civil Engineering and Chemistry Department California State University, Sacramento, California 95819

Abstract: The highest frequency near-infrared (NIR) combination bands for specimens of four species of mica—montmorillonite-beidellite, illite, chlorite, and kaolinite—were correlated with respect to Al2O3 content. A direct linear correlation was found between the combination band positions and the Al2O3 contents of the montmorillonite-beidellite series, which may be given as: ν̄ cm−1 = (5.38 ± 0.04) (% Al2O3) + (4412.8 ± 0.9). A similar linear correlation for muscovite is: ν̄ cm−1 = (6.10 ± 0.25) (% Al2O3) + (4434.1 ± 8.3).

Possible NIR band interferences are shown for different mineral mixtures, along with the correlation of different illites with muscovite. No combination bands were found in the frequency region 4425 cm−1 to 4625 cm−1 for specimens in which the Al2O3 content was only in the tetrahedral layer sites.

Key Words: Al content • Dioctahedral smectites • Micas • NIR spectra

Clays and Clay Minerals; December 1993 v. 41; no. 6; p. 639-644; DOI: 10.1346/CCMN.1993.0410601
© 1993, The Clay Minerals Society
Clay Minerals Society (www.clays.org)