266 B. B. Boltivood — Ultimate Disintegration 



An interesting radio-active mineral has been described by 

 Danne.* This substance is stated to be a phosphate of lead, 

 or pyromorphite, containing quantities of radium equivalent to 

 about 6 per cent of uranium. It is asserted, however, that 

 no uranium is present in the mineral, although considerable 

 deposits of uranium minerals are known to exist at no very 

 great distance in the same region where it occurs. According 

 to Danne, the pyromorphite is found in fissures through which 

 underground waters containing radium salts are constantly per- 

 colating, and he suggests that the radium contained in the min- 

 eral is derived from the water. It might also be conjectured 

 that the lead of the mineral has resulted from the disintegra- 

 tion of radium, the radium itself having been formed from the 

 disintegration of uranium in the neighboring deposits. 



Occurrence of Minerals. 

 It would seem possible that some general data on the disin- 

 tegration products of radio-active substances might be derived 

 from the study of the conditions under which the radio-active 

 minerals occur in nature. The following suggestions may 

 perhaps be of interest in this connection. The primary min- 

 erals found in the pegmatitic dikes include uraninite, thorite, 

 fergusonite, aeschenite, euxenite, columbite and monazite, all 

 of which, with the exception of columbite, f probably contain 

 thorium in greater or smaller proportions. The theory gener- 

 ally accepted by geologists is that the pegmatites were formed 

 under conditions of so-called hydro-igneous fusion, involving 

 high temperatures and the presence of considerable water 

 vapor which was prevented from escaping by the high pressure 

 due to incumbent masses of rock of great thickness. Assum- 

 ing the prior existence of considerable deposits of uranium 

 compounds at great depths, it would appear probable that in 

 an upheaval of deep-lying material, with the intrusion of the 

 plastic magma into the upper layers from below, the conditions 

 w T ould be favorable to the separation of the various constituents 

 of the already partially disintegrated uranium with the pro- 

 duction of new minerals representing new combinations of the 

 various elements present. Thus some of the uranium might 

 separate out as the oxide (uraninite), either quite free from 

 other elements or with admixtures of other isomorphous oxides 

 (thorium oxides and other rare earth oxides), while the thorium 

 might be greatly concentrated in the form of such minerals as 

 thorite and thorianite, containing mixtures of variable propor- 



* Compt. rend., cxl, 241 (1905). 



f The very common association of radio-active elements with niobium, 

 tantalum, etc., in minerals is possibly significant of some ultimate relation 

 between them. 



