282 ECONOMIC GEOLOGY 



TANTALUM 



Properties. Tantalum, symbol Ta, is an acid-forming element 

 closely allied to columbium, with which it is generally associated. 

 It is ductile, malleable, sectile, hard, tough, and readily with- 

 stands corrosion. Its melting point is 2250 C., its specific 

 gravity is 10.4, and its atomic weight is 181. 



Ores of the Metal. Tantalite, FeO, Ta 2 0s, is a tantalate of 

 iron. It occurs in orthorhombic crystals; is black with a cin- 

 namon-brown streak. It is the most important source of the 

 tantalum of commerce. 



Manganotantalite, MnO, Ta 2 Os, is a tantalate of manganese, 

 in which manganese has displaced the iron of normal tantalite 

 to a considerable extent, if not entirely. 



Ixiolite is a rare tantalate of tin. 



Samarskite, mentioned under Columbium, is a rare mineral 

 rich in tantalum. There are many tantalates of the rare earth 

 metals known in mineralogy, but they are rare minerals. 



Origin of the Ores. Tantalite, like its associate, columbite, 

 occurs as a primary mineral in the acid intrusives, as the granites 

 and pegmatites. Some of the rare tantalates are decomposition- 

 products of tantalite, and therefore of secondary origin. 



Geographical Distribution. Tantalite is found in practically 

 the same localities as columbite. Massive tantalite has been 

 found in Coosa County, Alabama; and manganotantalite of ex- 

 ceptional purity in western Australia. The American supply 

 is mainly obtained from Scandinavia and Australia. 



Separation. The columbates may be separated from the 

 tantalates by fusion with HKS0 4 or KOH, and treating the fused 

 mass with HC1 and metallic zinc. When diluted with an equal 

 volume of water, a permanent and intense blue coloration is 

 obtained. In the case of the tantalates thus treated, the blue 

 color soon disappears. 



Uses. F. L. Hess states that the only practical use to which 

 tantalum is put is in making filaments for incandescent electric 

 lamps. More than twenty thousand 20-candle-power incandes- 

 cent electric lamp filaments can be made from a single pound of 

 tantalum. The tantalum lamps used in America are manufac- 

 tured from imported tantalum. The cost of the metal is more 

 than $300 per pound. 



The metal is ductile, malleable, hard, tough, and strongly 



