W. P. Headden — Tantalate from So. Dakota. 295 



there was no distinguishable differences between the frag- 

 ments. After observing this fact, I took individual pieces, 

 broke them up and picked out enough of the clean mineral 

 to make the determination of the specific gravity, using a 

 pycnometer; the results varied as greatly as when I used 

 the Jolly balance. There were a few pieces, weighing 

 from 15 to 25 grams, that appeared to be clean and uni- r 

 form. I determined the specific gravity of these by sus- 

 pending them in water with the same results as before. 

 In a few instances I found a line through the sample that 

 suggested the possibility of a difference in the parts of the 

 piece. I broke these samples on this line and determined 

 the specific gravity of the separate parts. The greatest 

 difference that I found in this way was in the case of a 

 piece that weighed 15.4 grams. This piece showed a line 

 dividing it into two parts which differed slightly in tex- 

 ture, color, luster and iridescence. On placing a sharp 

 chisel on this line and giving it a quick tap, the piece split 

 in two almost equal parts which were free from mica, etc. 

 One piece was not so bright and clear a black as the other, 

 had a slightly granular fracture and a weaker iridescence. 

 The other piece had a pure, bright black color, conchoidal 

 fracture, metallic adamantine luster with a strong irides- 

 cence. The specific gravity of the former piece was 7.019 

 and of the latter 7.878 at 4° C. While this is the extreme 

 difference found in the specific gravity of two parts of a 

 comparatively small piece of mineral, it is not the only 

 instance of it. At first, I attributed this variation in the 

 case of small individual pieces to a mixture of samples, 

 that is, I supposed that several small masses had been 

 broken out and put together as a general sample of the 

 mineral. This may have been done but it does not follow 

 from the variation in the specific gravity of the individual 

 pieces. The columbites from the Etta mine showed 

 clearly that this mineral, from the same locality, varies 

 greatly in this respect. Even the individual crystals of a 

 group may vary both in specific gravity and composition. 

 The crystals at the Etta were large, weighing up to 10 or 

 more pounds, and were distinct individuals which may 

 have made a difference. In this case, the pieces are small 

 and there is no distinction of individual or even groups 

 of crystals. I have been unable to learn whether crystals 

 of this tantalate occur at the Old Mike Mica mine or not. 



