Infra-red spectra of gedrites have been measured in the hydroxyl region (3800–3500 cm−1). The spectra can be related to those of clinoamphiboles and of anthophyllites, and show the normal amphibole pattern of peaks whose intensities reflect the proportions of different cations in the adjacent octahedral sites. The absorption is weak especially in spectra of gedrites high in Al. Hyperfine splitting of peaks has been observed in anthophyllite spectra (Law, 1981) but the extent of hyperfine

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... ng in gedrite spectra is limited. The underlying baseline absorption, upon which the hydroxyl peaks are superimposed, becomes steeper and more awkward to estimate in gedrites. Some higher frequency peaks, probably arising from unit cells with A sites occupied by Na, are observed.