The alteration of radioactive minerals

  • T. C. Sarkar


The discordant lead ratios of uranium and thorium minerals gave rise to a number of unsuccessful but interesting ideas to explain them. A fresh attempt has been made here based on the alteration of radioactive minerals. The alteration of a radioactive mineral is distinguished from its transformation to the metamict state. The latter is entirely caused by physical agencies, whereas the presence of solution is essential for altering a mineral. Such a solution may exert (1) a solvent action; or (2) chemically react with a mineral; (3) sorption of substance from the solution as well as (4) ion exchange may take place. Each of these possibilities has been considered individually.

In (4) the supposition is made that part of lead in the radioactive minerals is present as plumbate just as uranium is partly present as uranate.Silica present in percolating waters as silicate may displace plumbate and uranate ions. This idea successfully explains (1) the high lead ratio obtained from altered uranium minerals, (2) low lead ratios from all altered minerals containing small quantities of uranium, (3) the alteration of uraninites, and (4) theraison d’etre of the “silica test” for the freshness of titano-tantalo-columbates.

Reasons are given for the belief that age indications of slightly altered monazites may be reliable, that the presence of alkalies in a primary radioactive mineral is a sign of its alteration, and that the process of alteration as considered here is a general one and applicable to non-radioactive minerals as well.

Holmes’ selective leaching hypothesis, Kirsch’s idea of magmatic rejuvenation to explain erratic lead ratios of Moss bröggerites and the idea of possible presence of common lead in radioactive minerals have been discussed and found unacceptable.


Uranium Thorium Uranium Mineral Solvent Action Common Lead 
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© Indian Academy of Sciences 1941

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  • T. C. Sarkar

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