Uraninite and Thorianite
WASSERSTEIN1 suggested that the generation by radioactive decay of Pb4+ of smaller ionic radii within the crystal lattice of uraninite caused a shrinkage in the unit cell proportionate to the geological age and the shrinkage was of the order of 0.0025–0.0041 Å. per hundred million years. The anomaly in the relation of cell dimensions of Bisundni and Gaya uraninites with the age, reported by Holmes2, was explained by Wasserstein3 by classifying uraninites into two different types—α-type for Bisundni uraninite and γ-type for Gaya uraninite, the latter being apparently anomalous and requiring heat treatment under oxidizing conditions in order to reduce the cell size to correspond to that of an α-type analogue. Wasserstein did not, however, state the temperature and period of heating and the conditions under which the cell size of γ-uraninite was reduced to correspond to age values consistent with those of the α-type.
The Age of Uraninite and Monazite from the Post-Delhi Pegmatites of Rajputana
Abstract Uraninite and monazite collected by Dr. H. Crookshank from pegmatites occurring respectively at Bisundni and Soniana (Rajputana) have been analysed for U, Th, and Pb by Mr. A. A. Srnales, and the isotopic constitution of the lead separated from each mineral has been determined by Dr. W. T. Leland and Prof. A. O. Nier. The three ages calculated from the uraninite ratios AcD/RaG, RaG/U and AcD/U are 740, 733, and 733 m.y. The monazite is considerably altered but the corresponding ratios indicate that its age lies between 700 and 865 m.y., which is consistent with the more reliable estimate determined from the uraninite. It is shown from tectonic evidence that the Delhi erogenic belt is younger than the Satpura belt (previously dated at about 900 m.y.) and that both are younger than the Aravalli and Dharwar belts.
Samarskite from Nellore District
Summary1.A typical sample of samarskite has been analysed and the results reported.2.The thoria content of the sample is 1·98%.3.The percentage of cerium earths present in this sample is relatively much smaller than found in samples from North America. Our sample contains 0·4% ceria.4.Hexavalent uranium has not been found in the sample but this is of no special significance.5.The radium contents is 1·0 gr. in 39· 71 tons and the Nellore samarskite is nearly as rich as Katanga Carnotite in this element.