506 



MINERALOGY 



little dilute HC1 and boiled with tin, yields a turbid brown color ; 

 when boiled with zinc yields a blue color. Fused with soda in O. F. 

 generally yields a green color (Mn) . Insoluble in acids. 



General description. Either crystalline or massive ; when 

 crystalline, in short stout prisms or of tabular habit, parallel to the 

 macropinacoid, at times acutely terminated by the pyramid (133). 



It often contains considerable amounts of tantalum, tungsten, 

 and tin. Tantalum and columbium form isomorphous compounds 

 which are associated in nature; tantalite (Fe . Mn) (TaO 3 ) 2 is a 

 mineral isomorphous with columbite, and it is rarely that one is 

 found without containing an admixture of the other crystallized 

 with it. They also form a series of compounds with the rare earths, 

 of which fergusonite (Y.Er.Ce)(Cb.Ta)O 4 is the most important. 

 It occurs at Rockford, Massachusetts; in North Carolina; and in 

 Llano County, Texas. 



Columbite is associated with cassiterite, wolframite, ilmenite, 

 magnetite, and other minerals found in pegmatites. It occurs in 

 the pegmatites of Maine ; brilliant crystals occur at Standish and 

 Middletown, Connecticut ; at various localities in North Carolina ; 

 in the pegmatites of the Black Hills in South Dakota, where crystals 

 weighing nearly two thousand pounds have been found ; here it is 

 also associated with cassiterite and it has been concentrated by the 

 same pneumatolytic agents. It is associated and contained in the 

 cryolite deposit of West Greenland. 



Tantalum has been used in the production of incandescent lamp 

 filaments, which are much more efficient than the carbon lamps. 

 Little or no columbite is mined in the United States. 



