ESR studies of E′ centres in geological flint

Properties of E′ centres of high geological age in flint from different locations have been studied. ESR spectra of γ-irradiated samples of heated and unheated Silurian and Eocene flint show thermally unstable components. The spectrum of one species could be simulated using the g values: 2.00164, 2.00059, and 2.00046. Two others deliver ESR-signals at g=2.0015 and 2.0012, respectively. These unstable components cannot be identified with any known E′ centres. About 50% of the ESR intensity of the E′ centres in unheated flint induced by artificial γ-rays is thermally stable. This effect is probably due to a steady state and might be useful for dating of unburned flint tools (“skinflint dating”).