CHAPTER IX 

 THE RARE METALS 



MOLYBDENUN, TUNGSTEN, TITANIUM, ZIRCONIUM, VANADIUM, 



URANIUM, COLUMBIUM, TANTALIUM, 



SELENIUM, TELLURIUM 



Molybdenum 



Properties. Molybdenum, symbol Mo, is one of the rarer 

 metals. Its specific gravity is 8.6, and its atomic weight 96. 



Mode of Occurrence. Molybdenum is a member of the same 

 elementary group with chromium, but its geological affinities are 

 widely different. It occurs as a primary constituent of the acid 

 rocks, like granite, rather than the basic rocks like peridotite, 

 the home of chromite. The metal does not occur free in nature 

 and is not widely diffused. 



Ores of Molybdenum. The sulphide of the metal, molyb- 

 denite, MoS 2 , is the most important ore. This mineral closely 

 resembles graphite, but may be easily distinguished from it. 

 Graphite is quickly copper-plated when in contact with a strip 

 of zinc in a solution of CuSO 4 ; molybdenite is slowly copper- 

 plated under the same conditions. Graphite is unaffected by 

 HNO 3 ; but molybdenite is oxidized to MoOs. The molybdates of 

 several metals are well known as natural minerals: Wulfenite, 

 PbMoO 4 ; powellite, CaMoO 4 ; pateraite, CoMoO 4 ; belonesite, 

 MgMoO 4 ; and molybdic ocher, Fe 2 (MoO 4 ) 3 ,7|H 2 0. The oxide 

 of molybdenum occurs as a secondary mineral, molybdite, MoO 3 . 



Origin of Ores. Molybdenite, the most important source of 

 the metal, is of primary origin. According to G. O. Smith, it 

 occurs at Cooper, Maine, as an impregnation deposit. It occurs 

 in the pegmatite dikes and their associated granites. The oxides 

 and ocher are always of secondary origin. 



Character of Ore Bodies. A. R. Crook has observed large 

 masses of molybdenite in quartz veins in granite at Crown Point, 

 Washington. The author has observed molybdenite on the east- 

 ern coast of Newfoundland in large quartz veins traversing 

 sandstones and conglomerates. In Maine it occurs in pegmatite 



268 



