Luminescence, induced by dehydration and by wetting with hydrazine and unsymmetrically substituted hydrazine, and related ESR spectra have been observed from several kaolinites, synthetically hydrated kaolinites, and metahalloysites. The amine-wetting luminescence results suggest that intercalation, not a chemiluminescence reaction, is the luminescence trigger. Correlation between dehydration-induced luminescence and g = 2 ESR signals associated with O−-centres in several natural halloysites, and concurrent diminution of the intensity of both these signal types as a function of aging in two 8.4 Å synthetically hydrated kaolinites, confirm a previously-reported relationship between the luminescence induced by dehydration and in the presence of O−-centres (holes, i.e., electron vacancies) in the tetrahedral sheet. Furthermore, the ESR spectra of the 8.4 Å hydrate showed a concurrent change in the line shape of the g = 4 signal from a shape usually associated with structural Fe in an ordered kaolinite, to a simpler one typically observed in more disordered kaolinite, halloysite, and montmorillonite. Either structural Fe centres and the O−-centres interact, or both are subject to factors previously associated with degree of order. The results question the long-term stability of the 8.4 Å hydrate, although XRD does not indicate interlayer collapse over this period. Complex inter-relationships are shown between intercalation, stored energy, structural Fe, and the degree of hydration which may be reflected in catalytic as well as spectroscopic properties of the clays.