The Intensity of Amphibole OH Bands in the Infrared Absorption Spectrum

Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125-2500, USA

Polarized IR spectra of single-crystals of amphiboles show that the molar absorptivity of the fundamental vibrational OH band is strongly wavenumber dependent. The intensity increases by a factor of 1.6 from 3674 cm^-1 (tremolite endmember; MgMgMg) to 3618 cm^-1 (grunerite endmember; FeFeFe). Spectra obtained from Ca and Fe-Mg amphiboles consist of sharp, well-resolved bands on a well-defined back ground. The high intensity of the OH bands in Ca and Fe-Mg amphiboles makes it sometimes necessary to thin the samples to under 2 mm thickness, whereas alkali amphiboles can be measured at 25-50 mm thickness.