Radioactive Nodules from Devonshire, England

Summary

Globular concretions surrounded by bleached haloes were found in Permian beds west of Budleigh Salterton, Devon. In their interior a light, sandy matrix is impregnated by a dark hard material in radial and concentric sheets. Contact photographs of a plane section show a distribution of radioactive material closely connected with the structure of the black impregnation.

The radioactive substance was found to be centred in a thin amorphous film of a complex uranium-vanadate at the boundary between the dark and the light portions of the nodules. The total proportion of radioactive elements present in the concretions corresponded to 0.3%—0.5% uranium or 10-⁷% radium. The properties of the dark parts of the nodules are caused by an apparently amorphous impregnation of vanadium oxides, various other ores also being present in smaller concentrations. A classification of nodules according to their internal structure is proposed; three different varieties are distinguished and the possibilities of their origin are being discussed.

It was found that the chemical composition of the bleached haloes does not differ essentially from that of the red clay, and that the bleached haloes contain a smaller proportion of ferric iron, whereas the percentage of ferrous iron is the same as that in the red clay. The thickness of the haloes is neither constant nor in any constant numerical relation to the diameter of the nodules. It is suggested that the radon produced in the nodules and diffusing from their surface might be responsible for the formation of the bleached haloes.