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



Under these conditions one is compelled to use the identi- 

 cal piece for analysis that was used in determining the 

 specific gravity. The description of the samples analyzed 

 has been given in sufficient detail : 



Analysis of a Tantalate from the Old Mike Mica Mine. 





Sp. gr. 

















At. Eatio 





at 4° C. 



Ta>0 5 



Cb 2 5 



Ti0 2 



Sn0 2 d 



FeO 



MnO 



Total 



Fe to Ta 



l,a 



6.954 



69.55 



8.63 



1.50 



5.29 



10.84 



4.19 



100.00 



1:2.06 



2.b 



7.019 



76.08 



5.49 



2.84 



0.22 



14.16 



1.21 



100.00 



1:1.96 



3. 



7.180 



77.24 



6.97 



0.81 



1.18 



13.60 



1.02 



100.82 



1:1.95 



4. 



7.468 



78.28 



5.56 



1.33 



0.28 



13.35 



1.22 



100.62 



1:2.05 



5. 



7.794 



79.50 



4.32 



0.92 



0.32 



13.42 



1.56 



100.04 



1:2.02 



6. 



7.878 



81.40 



3.69 



0.58 



0.12 



12.55 



1.73 



100.07 



1:2.03 



7. 



7.975 



83.57 



1.97 



trace 



0.10 



13.28 



1.19 



100.10 



1:1.99 







Tapiolite from Prospect in 



Minnehaha Gulch. 





8.c 



. 7.190 



77.23 



5.18 



1.38 



0.32 



14.84 



0.42 



100.00 



1:1.95 



a Eecalculated after deducting 1.52% tin-stone. 

 b Eecalculated after deducting 1.56% tin-stone. 

 c Eecalculated after deducting 0.88% tin-stone, 

 d Sn0 2 includes traces of W0 3 . 



Analyses 2 and 6 are parts of the piece weighing 15.4 

 grams previously mentioned and show that they differ 

 greatly in composition as well as in specific gravity. 

 Analyses 3 and 4 are parts of another piece, that weighed 

 25 grams and they too show that they vary in the same 

 manner. 



Analysis 8 is a portion broken off of the crystals of 

 tapiolite found not very far from this Old Mike Mica 

 mine locality. The specific gravity of this group of crys- 

 tals and of the pieces broken off of the base of them was 

 determined several times at 18° and the deviation found 

 was from 7.15 to 7.21. The specific gravity of the whole 

 group was found to be 7.20. The average of all deter- 

 minations made reduced to 4° C. is 7.190, which I have 

 taken as that of the material analyzed. Analyses 3 and 8 

 have very nearly the same specific gravity and are almost 

 the same in composition. These samples are not from the 

 same locality, but the localities are not more than three 

 miles from one another and are in the same gulch. The 

 agreement in composition is what we should expect if the 

 relation between the specific gravity and composition in 

 these minerals is as intimate as we suppose it to be ; but 

 it does not prove the mineralogical identity of the two 

 samples though it may reasonably be taken to suggest 

 this. 



. 



