gsminmag Mineralogical Magazine Mineralogical Magazine 0026-461X Mineralogical Society 10.1180/minmag.1979.043.325.14 The Effect of Aluminium on the Infra-Red Spectra of 7 Å Trioctahedral Minerals1 Serna Carlos J. 2 White Joe L. Department of Agronomy, Purdue University West Lafayette, Indiana 47907 Velde Bruce N. Laboratoire de Petrographie, Faculté des Sciences, 9 Qual Saint-Bernard, Paris 5me, France

Journal paper 7132, Purdue University Agricultural Experiment Station, West lafayette, indiana 47907.

On leave from Instituto de Edafologia, C.S.L.S. Mardrid, Spain.

 3 1979 43 325 141 148 2 5 1978 5 9 1978 Copyright © 1979, The Mineralogical Society 1979 Summary

The substitution of 2A13+ for Si4+ +M2+ (M = Mg or Ni) has been studied by infra-red spectroscopy in 7 Å trioctahedral minerals over the composition range from Al = 0.00 to Al = 2.00. Significant differences are observed in the infra-red spectra and these make possible an estimation of the amount of Al in tetrahedral coordination. The most striking effect of the substitution is observed in the stretching vibrations of the outer hydroxyl groups and that of the silicate anion.

The aluminous Mg-serpentines can be readily distinguished from their analogues, the aluminous Niserpentines, by the absence of the Mg-OH absorption band between 570 and 615 cm−1 in the latter.