IT has been shown in previous publications1 that at least some of the maxima in the absorption spectra of natural coloured fluorites coincide with those obtained by artificial irradiation, thus completing the proof that the natural colour is due chiefly to radioactivity. Different fluorites show, however, very different colours and absorption spectra. This might be due in part to the fact that the conditions of formation of these minerals may vary greatly. It seemed, therefore, to be of interest to study the bands of different colour which are frequently seen in the same sample of fluorite, in which case the conditions of formation cannot have varied so much.