224 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1925 



amply supply the world. Even these laboratories are forced to 

 restrict their production that tlieir reserve of radium may not use- 

 lessly augment. 



Kadium comijounds constitute the most expensive bodies of cur- 

 rent commerce. The price of radium oscillates about 1,000,000 

 francs per gram, while platinum reaches 80 francs. M. Chaumet, 

 the well-known jeweler, has told me that a ruby may reach 750,000 

 francs per gram while a perfect pearl weighing 50 grains would sell 

 for 2,500,000— -say 1,000,000 francs per gram. 



HADIFEUOUS MINERALS 



Radium is scattered throughout the rocks of the earth's crust 

 but generally in infinitesimal quantities. Almost all the samples 

 examined by the most sensitive methods show an extremely weak 

 radioactivity; only the pure limestones and the quartz sands are 

 nearly inactive. The waters of springs, mineral w^aters which have 

 been in contact with radiferous earth, are almost always more or 

 less radioactive. According to direct measures of Strutt, the ter- 

 restrial crust contains on the average about 4X10'*^ grams per meter. 

 The richest rocks are the igneous granites. The sedimentary rocks 

 are much less rich. All radioactive materials are composed of 

 granitic rocks or have been derived from them. 



The oldest or primary uraniferous minerals have remained un- 

 altered in the original rocks — like fergussonite, thorianite. By the 

 action of water upon these primary rocks, new minerals have been 

 formed, sometimes within the original beds, sometimes beside them. 

 A great concentration .of uranium may thus have resulted. Pitch- 

 blende is typical of the secondary rocks. Finally, atmospheric 

 agents, working upon the two preceding classes of minerals, have 

 formed a third more recent class of which chalcolite, autunite, and 

 carnotite are typical. 



Pitchblende is essentially an oxide of uranium, UgOs, mixed with 

 numerous impurities. The oxide occurs sometimes onl}'^ as a trace, 

 sometimes in more massive formation. Many elements occur among 

 the impurities. The following table gives the principle components 

 of a rich sample from Joachimstahl : 



UsOs 75 



PbS 5 



SO, 3 



CaO 5 



FeO :{ 



MgO 2 



The veins of the Belgian Congo have given birth, through the 

 intermediation of atmospheric agents, to a whole new series of com- 

 pounds recently discovered and studied by Professor Schoep of 

 Gand. 



