Radium and Geology

Abstract

AFTER reading Arrhenius's vivid account1 of the bombardment of the earth by electrically charged solar dust, one is prepared to appreciate Prof. Joly's hypothesis as set forth in his letter in NATURE of January 24. On the other hand, Mr. Strutt's analysis of granite affords strong support to the view that the radium it contains is of terrestrial origin. The concentration of this constituent in the biotite might conceivably be due to the absorption of percolating water containing radium in solution, but not in the zircon, a mineral which is as impermeable as quartz. A mineral analysis of Cornish granite from Penrhyn, made by Miss Davies in our geological laboratory, gave the following results:—orthoclase, 24.62 per cent.; albite, 13.42 per cent.; quartz, 40.23 per cent.; muscovite, 10.05 per cent.; biotite, 11.46 per cent.; magnetite and zircon, 0.16 per cent. The heavy portion of the Cornish granite analysed by Mr. Strutts which was insoluble in hydrochloric acid, consisted of silica hydrate and zircon, and if the latter mineral was present to the extent of 0.16 per cent. only, it must have contained, judging from the analysis, 0.637 × 1012 gram of radium per gram, or a little less than was found in crystals of zircon from North Carolina. In the consolidation of granite, the zircon crystallises out first, then the biotite, next the muscovite, afterwards the albite, and, finally, the orthoclase and quartz; but the concentration of radium diminishes in a similar order, a correspondence that can hardly be the effect of chance.