A serie of phlogopites having as varied a range of structure as possible and the principal types of stacking that are known have been submitted to the sodium cobaltinitrite treatment. For comparative purposes other micas with different compositions were also studied, e.g. lepidolite, zinnwaldite, muscovite, glauconite and phengite. The transformation of mica to vermiculite was possible with all the phlogopites and also for the glauconite and phengite. The most important finding was that the behaviour of the various micas that were treated does not provide information on the influence of the crystallochemical composition.Sommaire : Une série de phlogopites présentant une gamme de constitutions aussi variées que possible et les principaux ...