RADIOACTIVE MINERALS IN SOUTK AFRICA. 45 L 



Plate 12, c and d, from Embabaan after an exposure of seven 

 an4 15 days in each case. 



As stated above, monazite has been principally used for the 

 preparation of thoric nitrate. In the course of close investi- 

 gations of the tailings of the monazite conducted during recent 

 years, Professor Otto Hahn, of Berlin University, discovered 

 another very powerful radio-active substance, which he called 

 mesothorium. This substance has been found to be as effective 

 in the treatment of cancer as radium itself. But the " life " 

 of mesothorium is only 14 to 16 years, whereas the " life " of 

 radium is about 2,000 years. 



^SCHYNITE. 



This is a comparatively rare n.ineral, and has not yet been 

 observed in large deposits or formations. At Embabaan 



jeschynite occurs together with monazite, euxenite. fergusonite, 

 and tin stone, as water-worn fragments up to 20 grammes in 

 weight. It is of a somewhat complex composition, being a 

 titano-niobate of the metals of the cerium group, containing as 

 accessory admixture thoric dioxide, which may rise to 28 per cent. 

 The two specimens from Embabaan analysed in the South 

 African College Chemical Laboratory contained 16.2 per cent, 

 and 16.7 per cent, of thoric dioxide. 



The action of this seschynite on the photographic plate 

 after exposure of seven and after 15 days respectively, is shown 

 in Plate 13. fl and b. 



Euxenite. 



This is one of the rare minerals found in the alluvial tin- 

 ore deposits near Embabaan. The specimens which were 

 analysed had been presented by Mr. R. N. Kotze, Government 

 Mining Engineer, Johannesburg. Euxenite has not yet been 

 found in large deposits. It is a titano-niobate of erbium, 

 yttrium, and cerium with an admixture of i per cent, to 12.12 

 per cent, of uranic trioxide. Three specimens of euxenite 

 from Embabaan were analysed, and were found to contain only 

 1 .79 per cent., 2.05 per cent, and 2. 12 per cent. — on an average 

 1 . 99 per cent, uranic trixide. 



The action of this euxenite on the photographic plate was 

 very distinct. Plate 13, r, was obtained after an exposure of 

 seven days. 



Fergusonite. 



In 1897 the presence of this rare mineral was observed in 

 the alluvial tin ore deposits of Embabaan. It has not been 

 observed anywhere in workable quantities. It is a tantalo- 

 niobate of yttrium, erbium, cerium, and lanthanum, with an 

 admixture of i per cent, to 6.21 per cent, of uranic trioxide. 

 One specimen of this mineral from Embabaan contained only 

 1.28 per cent, of uranic trioxide. 



