KXCESS OF FERROUS OXIDE AND MANOA"NOU8 OXIDE. 39 



considerable excess of iron on analysis. Specular hematite or 

 magnetite, in particles too small to be easily distinguished, may occur 

 in the ore, and the presence of one or both of these minerals may 

 account for the surplus iron shown in some determinations. 



In those wolframites which contain tantalum and columbium 

 columbite may furnish a part of the apparent excess of iron. Micro- 

 scopic examinations made by reflected li^ht on polished and etched 

 specimens of clean black ferberite show none of the differences in 

 texture to be expected if such other minerals were present. There 

 are, however, minute cavities which may be partly filled with iron 

 minerals. Manganese dioxide, though in less quantity than iron 

 oxides, is commonly associated with the ores, but its presence on the 

 lighter-colored hiibnerites should be easily distinguishable. The 

 possibility of FeO and MnO being held in solid solution in the minerals 

 of the wolframite series suggests itself, but no proof of this has been 

 found. 



It is to be noted that if the analyses given had been recalculated 

 by first satisfying the FeO with WO 3 , and then combining the 

 remainder of the WO 3 with the MnO, the excess of the FeO would 

 disappear in most of the analyses and there would be an excess of 

 MnO. However, as just stated, manganese oxide occurs with the 

 wolframites in much less quantity than iron oxide, and for this reason 

 in recalculating an analysis it is best to first satisfy the MnO with 

 WO 3 . It appears, therefore, that though some of the wolfrainitesi 

 may carry an excess of FeO, and a few an excess of both FeO and! 

 MnO, most if not ah 1 of the apparent excesses are due to impurities] 

 present in the material analyzed and to errors of analysis. 



Many careful analyses of well-selected minerals and many examina- 

 tions by metallographic methods must be made before a real excess 

 of FeO or MnO in the wolframites can be demonstrated. 



