Abstract

By studying the NMR signals of protons and fluorine in a series of crystalline phlogopites at various frequencies and angles, it has been possible to differentiate among various octahedral associations. In samples with continuously variable amounts of fluorine and iron, we show that the OH groups, rather than the fluorine ions, are in direct coordination with the iron. This anionic segregation relative to Fe2+ is also confirmed by the observation of fluorine pairs, which most probably form homogeneous fluorine domains. This local ordering of octahedral ions is an important parameter in the study of cohesion of layered silicates.

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