Abstract: The i.r. spectrum of K depleted biotites (structural OH stretching range) has been studied with monocrystals equilibrated at various water contents. Prior to spectroscopic measurements, the samples were submitted to deuteration treatments which displaced the hydration water spectrum to the OD region and made it possible to observe the behaviour of the structural hydroxyls without interference from hydration water.
In these conditions it was shown that the high frequency absorption of K depleted biotites (N + I bands) is the sum of two absorptions: the first corresponds to the initial mica spectrum, the second corresponds to the hydrated phase in which component bands (according to Vedder and Wilkins) are shifted by 36 cm−1 towards low frequencies.
Simultaneously it was shown that low frequency bands (V bands) decreased in intensity. This unexpected observation has been explained by a partial deuteration of structural OH, which takes place during the preliminary contacts of the samples with D2O vapour.