280 ECONOMIC GEOLOGY 



deposits in sandstones. It occupies the interstices between the 

 grains, and occurs in thin coatings in the cracks and crevices of 

 the rocks. In some instances, lumps of several inches in thick- 

 ness have been obtained. These lumps are very pure. 



Geographical Distribution. Uraninite and gamotite occur in 

 Montrose County, Colorado, and also in Utah. Pitchblende is 

 found in Gilpin County, Colo. Carnotite occurs in Montrose, 

 San Miguel, Dolores, Rio Blanco, and Routt Counties, Colo., 

 and in the eastern part of Utah. 



Geological Horizon. In southwestern Colorado, the carnotite 

 deposits are in Jurassic sandstones, and in northwestern Colorado 

 in Cretaceous sandstones. 



Extraction of the Metal. Uranium salts have been extracted 

 at the Haynes plant near Cedar, Colo. ; but the haul both for ore 

 and supplies is long and expensive. The ore is of low grade, and 

 the problem of commercial extraction is difficult. 



Uses. Uranium, unlike the other rare metals considered above 

 in this chapter, does not find its most important use in the manu- 

 facture of steel. This use will be considered later. 



Uranium minerals and their salts are radioactive. They have 

 given rise to the study of radiology, and to a new method for the 

 determination of the age of the earth through radium emana- 

 tions. A careful study of the data published along this line 

 places the age of the earth at approximately 100,000,000 years. 

 A pocket-knife, keys, coins, or any piece of metal may be covered 

 with uraninite and placed on a photographic plate in a dark 

 room; and in a few days, upon the development of the plate, 

 photographs of the objects will be obtained. 



Uranium hardens and toughens steel, like its associate, vana- 

 dium. It is used in Germany in the manufacture of steel and 

 ferro-alloys, and of gun-barrels. 



The salts of uranium are used in the manufacture of pottery 

 glazes and iridescent glass. The double acetate of uranium and 

 sodium is used in the determination of phosphates. Uranyl 

 acetate is used in medicine as a precipitant for proteids, and in the 

 chemical laboratory in the volumetric determination of zinc. In 

 this determination, the nitrate may be substituted for the acetate. 

 The nitrate is also used in the manufacture of glazes; in photog- 

 raphy; in the chemical laboratory in the determination of arsenic 

 and phosphoric acid, and in the detection of morphine. The 



