Cube-Edges of Uraninites as a Criterion of Age

Abstract

I HAVE suggested that there is a progressive reduction in the size of the unit cell of uraninite-thorianites with time¹. The ionic radius of Pb⁴⁺ is appreciably smaller than those of U⁴⁺ and Th⁴⁺. The decay of the parent element causes its substitution by radiogenic lead within the crystal lattice; because of the differences in sizes of the ions, a shrinkage results. It is therefore likely that this factor can be utilized for indicating the relative ages of uraninites after these have been subjected to an X-ray powder examination. No great accuracy can be envisaged, but such a method would be more accessible to geologists than the highly refined mass-spectrographic one, which can be practised in very few laboratories in the world.