404 BULLETIN 131, UNITED STATES NATIONAL MUSEUM 



of these compounds is obviously very difficult and hardly appears 

 practicable in view of the uncertainty concerning the stage of oxida- 

 tion of the iron and uranium. There is more Ti0 2 present than is 

 required to form normal titanates of all the bases, but not enough 

 to form metatitanates without taking some uranium as the basic 

 radicals UO and U0 2 . To secure an exact balance any excess of 

 TiO, may be reduced to the form of a titanyl metatitanate TiO.Ti0 3 .' 

 The mineral may be represented as a hydrated metatitanate of various 

 bases, thus: (Ca,Fe,UO,TiO)TiO s .(Th,Zr,UO) (Ti0 3 ) 2 .Yt 2 (Ti0 3 ).H 2 0. 

 Without implying exact molecular ratios the proportions of these 

 four would be about 6:8:1:3, respectively. It is to be remembered, 

 however, that the state of oxidation of the iron is unknown and this 

 ignorance introduces uncertainty in these proportions. Nor is it 

 known whether minerals of this kind should be considered as mixed 

 crystals, solid solutions, or salts of complex acids. The brannerite 

 contains more uranium than any similar mineral except pitch- 

 blende. Unlike most others it contains no tantalum or columbium 

 and is very high in titanium. 



THE NIOBATES-TANTALATES 



The minerals of the several groups included under the heading 

 Niobates-Tantalates have been found in Idaho, with the exception 

 of columbite, only as grains and larger masses in the concentrates 

 from placer gravels, mainly in Boise County, but also in Custer and 

 Clearwater Counties. 



The available information regarding these minerals has been, 

 in part, previously presented in an earlier publication by the writer. 15 

 The minerals mentioned below as tentatively identified in these 

 sands include fergusonite, columbite, polycrase, hjelmite, aeschynite, 

 samarskite, pyrochlore, and euxenite. Of these, columbite is de- 

 finitely identified and brannerite, a new mineral, has been described 

 in detail above. The identifications of polycrase and samarskite 

 are partially established by crystal form while the other identifica- 

 tions are little better than mere surmises. The mineral listed and 

 described as polycrase is available in amount sufficient for chemical 

 analysis but the other minerals are present only as small grains and 

 their isolation in pure form in amount sufficient for analysis would be 

 a matter of difficulty. The identification of minerals of this class is 

 difficult, since most of them are isotropic, many of them are opaque, 

 and all have very high indices of refraction. Furthermore none 

 have characteristic blowpipe reactions or chemical peculiariarities 

 of diagnostic value. The analysis of any mineral of the group is a 



15 Earl V. Shannon. Mineralogy of some black sands from Idaho, etc. Proc. U. S. Nat. Mus., vol. 60, 

 art. 3, pp. 1-33. 



