Minerals containing Columhium. 



413 



other, consisting of the specimens from Finland, discovered 

 by Nordenskjold, and which give a cinnamon brown powder 

 when pounded, he calls tantalite. He mentions a fine cry- 

 stal of columbite in the Royal Collection at Berlin, in which 

 the faces on both sides of the crystal are exposed ; but he 

 was not able to measure its angles, nor to determine its 

 structure. 



The specimen of Bohemian columbite in my cabinet is a 

 portion of a crystal about an inch in length, and wanting 

 both the terminations. Its length was originally about 

 1^ inch ; but I broke a fragment off it to enable me to 

 subject it to a chemical analysis. 



Its colour is black, but it is lighter than that of torrelite. 

 And, when reduced to a fine powder, it still retains its 

 black colour. But, when the powder is heated to redness, 

 it changes to chocolate brown like that of torrelite ; though 

 it loses only ^(jVoth of its weight. 



The structure is foliated. Only two faces of the crystal, 

 which is a flat four-sided prism, are smooth enough for 

 measurement. They meet at an angle of 90^, shewing that 

 the prism is rectangular; and Mr. Brooke has ascertained, 

 that the primary form is a right rectangular prism. The 

 faces of the prism are streaked longitudinally. 



The following are the measurements by Mr. Brooke of a 

 crystal in his possession : 



