Abstract
This paper gives an account of measurements of thorium haloes in biotite, made with the halo photometer. This apparatus, which has been earlier applied to uranium haloes, gives a permanent record of the structure of a halo, yielding ring diameters and intensity of blackening throughout the halo. Thorium haloes are very rare compared with those due to uranium. Out of more than a hundred biotites examined up to the present, only one gave a reasonable number of clearly defined haloes due to thorium. This material came from the Star Lake district in Manitoba, near the Ontario boundary. It was a brown biotite occurring as easily cleavable crystals a few mm. in diameter. Haloes were not very plentiful in the small amount of material available, but they were in rich variety including thorium, uranium, and compound uranium-thorium, as well as several other types of halo, which will be dealt with in another paper. A few good thorium haloes were also found in a brown biotite from Pierrepont, St. Lawrence Co., N.Y., and one or two more have been recognized in other biotites.
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Schedule a callMore From: Proceedings of the Royal Society of London. Series A - Mathematical and Physical Sciences
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