W. P. Headden— Tantalate from So. Dakota, 299 



ing line between distinct mineralogical individuals , for 

 the tapiolite with a specific gravity of 7.19 is tretragonal 

 and well crystallized. 



Another thing that is shown is that the tantalate is 

 an iron salt whereas the columbites with a tendency to 

 a high manganese content are mixed. In the tantalate 

 the ratio of Fe to Mn increases from 5.2 in the sample 

 having a specific gravity of 6.954 to 11 :1 in those having a 

 specific gravity around 7.9, and to 35 :1 in the tapiolite. 

 This ratio in the columbites is reversed, being a little less 

 than 3 :1 in the Harney City columbite and 1 :3 in those 

 from the Old Mike locality. The columbite from Tin 

 Mountain is a different mixture in which the Fe:Mn is 

 as 4:2, but at the same time the tantalum present has 

 risen to an amount equal in atomic equivalence to the 

 columbium. The columbites from the Harney Peak dis- 

 trict that I have studied are all intermediate in respect 

 to these ratios, ranging for Cb :Ta from 1 :1 to 6 :1 while 

 the Fe :Mn ratio is from 8 :1 to 1 :1. There is one instance 

 in which it is reversed and becomes 1 :2 in a sample that 

 represents a single mass of columbite in the Sarah mine. 

 These relations hold for such of the Black Hills colum- 

 bites as I have examined. This mineral from different 

 districts has a different, but for the district in general, a 

 characteristic composition. This does not apply in com- 

 paring the mineral from the Black Hills with samples 

 from other localities, even in cases in which the specific 

 gravities are approximately the same. In the case of a 

 columbite from Morrison, Colo., with a specific gravity 

 of 5.383, we have practically no tantalic acid and an 

 Fe :Mn ratio of 8 :7 whereas a columbite from the Old 

 Mike with a specific gravity of 5.421 and very little tan- 

 talic acid has an Fe :Mn ratio of approximately 1 :3. 

 It would be inadmissible to compare minerals of different 

 specific gravities. 



Colorado Agricultural College, 

 Fort Collins, Colo. 



