298 W. P. Headden — Tantalate from So. Dakota. 



metallic in those from Tin Mountain. These latter con- 

 sisted of small fragments of plates, and one larger piece 

 that weighed 17.33 grams. The specific gravity of these 

 differed; that of the larger piece was 6.725 and that of 

 the plates was 6.845 at 4° C. The characteristics of these 

 pieces were those of typical columbites except that the 

 f ractnre at the edge of the larger piece was distinctly con- 

 choidal. The inner side and the surfaces exposed by 

 cleaving this piece in two parts showed a fine granular 

 fracture. I do not know the details of these occurrences. 

 The specific gravity has a wider range than I have met 

 with in other samples, namely from 5.201 to 6.845. The 

 former is the lowest and the latter the highest that I have 

 found for a columbite from any locality. The lowest that 

 I have found for a tantalate is 6.954. The sample with 

 this specific gravity differed as widely in its physical 

 properties from the columbites as the tantalate having 

 a specific gravity of 7.975 and was a fragment picked out 

 of the same lot. Its composition is that of a tantalate 

 having the formula 5FeTa 2 6 .FeCb 2 6 compared with 

 8FeTa 2 Q 6 .7FeCb 2 6 for the columbite having the specific 

 gravity of 6.845. 



In the following table of analyses of columbites num- 

 bers 1, 2, and 3 are from the Old Mike locality, number 4 

 is from Harney City and numbers 5 and 6 are from Tin 

 Mountain. Number 4 is from Pennington Co., the others 

 are from Custer Co. 



Analyses of Columbites. 





Sp. gr. 

















Eatio 





at 4° C. 



CbA 



Ta 2 5 



Ti0 2 



Sn0 2 a 



FeO 



MnO 



Total 



Fe:Cb 



1. 



5.201 



68.00 



9.88 



0.53 



0.88 



5.45 



14.79 



99.53 



1:1.99 



2. 



5.421 



67.20 



10.10 



0.92 



0.96 



5.96 



15.08 



100.22 



1:1.92 



3. 



5.496 



63.90 



13.74 



0.80 



0.54 



5.92 



14.95 



99.85 



1:1.91 



4. 



6.444 



34.60 



46.02 



1.52 



0.38 



13.32 



4.31 



100.15 



1:1.92 



5.* 



6.725 



27.22 



53.47 



1.30 



0.44 



11.91 



5.66 



100.00 



1:1.91 



6. 



6.845 



28.81 



53.67 



1.63 



0.38 



12.00 



5.20 • 



100.69 



1:1.98 



a The Sn0 2 contains W0 3 in quantity up to 50% of the Sn0 2 present. 

 t>Lime equal to 0.48% deducted. 



These analyses show, if those of the columbites are 

 placed first, a gradual increase in the specific gravity from 

 5.2 to 7.94 with a regular increase in the amount of tan- 

 talic acid. This is still true even when we pass the divid- 



