Hess and Wells — Occurrence of Struverite. 435 



Pirsson.* Their material was probably identical in character 

 with that here described. 



In addition to the forms as illustrated by Pirsson, there is 

 often present, on the crystals examined, a narrow face of e 

 between a and a. The measurements on which the identifica- 

 tions are based follow. 





Measured. 



Calculated for r 



e 



S — 27°51' — 28°59' 



28°26' 



e 



a = 56 30 — 51 20 



57 13 



s 



s' = 55 57 — 56 50 



56 52 



a 



a — 66 10 — 66 30 



65 34 



a 



e — 10 30 



8 21" 



The mineral does not appear to be radioactive to any con- 

 siderable degree, but after 15 days' contact of a polished speci- 

 men with the sensitive side of a photographic plate, the micro- 

 cline surrounding the striiverite gave a distinct radiograph, 

 the plate remaining unaffected under the struverite. 



Although it occurs in considerable quantity, the mineral 

 gives little promise of having commercial value as an ore of 

 tantalum, owing to the high titanium content. 



Chemical Analysis. (R. C. W.) 



The mineral was separated from the gangue almost com- 

 pletely by crushing and panning. The resulting black grains 

 were dried at 100°. Under the microscope there were visible 

 only the black opaque mineral and a few grains of silica. 



Suitable tests showed that the essential constituents were 

 titanium, tantalum, columbium, and iron. There were small 

 amounts of tin and silica and a trace of aluminum. Phosphorus, 

 calcium, manganese, molybdenum, rare earths, tungsten, and 

 heavy metals were proved absent. It was concluded that 

 zirconium was also absent because after repeated precipitations 

 of the sulphates of the bases with hydrogen peroxide in the 

 presence of a phosphate no residue finally remained, f With 

 less than one per cent of sulphuric acid present in this last 

 operation, much tantalum and titanium, and to a less extent 

 columbium, are precipitated by the phosphate. But the separa- 

 tion of zirconium is based on the fact that it is almost certainly 

 precipitated in the presence of one per cent of sulphuric acid 

 and possibly in the presence of even more. 



The density of the fragments was found by the pycnometer 

 to be 5*25. Since the approximate density of titanium oxide is 

 4/0, of iron titanate 4*8, of iron columbate 5 - 9 and of iron tanta- 



*Headden, W. P. and Pirsson, L. V. on Black Eutile from the Black Hills. 

 This Jour., 3d ser., vol. xli, 1891, p. 249. 



f W. F. Hillebrand, Bull. 305 U. S. Geol. Survey, p. 141. 



