THE INTENSITY OF AMPHIBOLE OH BANDS IN THE INFRARED-ABSORPTION SPECTRUM

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 background. The high intensity of the OH bands in Ca and Fe-Mg amphiboles makes it sometimes necessary to thin the samples to under 2-mu-m thickness, whereas alkali amphiboles can be measured at 25-50-mu-m thickness.