Hess and Wells — Occurrence of Struverite. 441 



with his titanium. Owing to the unsatisfactory state of the 

 analytical methods applicable to these elements, it seems likely 

 that heretofore small amounts of tantalum or columbium may 

 often have been overlooked in titanium minerals. 



The analysis yields no simple formula. Apparently one 

 molecule of FeO is present to one molecule of (Ta,Cb)„0 6 , but 

 TiO„ lies between 6 and 7 molecules. The formula approxi- 

 mates roughly to Fe(Ta,Cb) a O,.6TiO a . 



Classification of the mineral. (F. L. H. and R. C. W.) 



The tetragonal minerals containing titanium, tantalum, 

 columbium and iron evidently form a series with a group at 

 one end to which the name ilmenorutile is given and a group 

 at the other end represented by the mineral described in this 

 paper. Prior and Zambonini's* mineral has a nearly medial 

 composition, but really belongs to the ilmenorutile group. 

 Ilmenorutile, when first described by P. von Eremeyev,f was 

 supposed to be a rutile containing " up to 10 per cent, or more 

 of Fe,0 3 ." Brogger4 in later analyses under improved con- 

 ditions, found ilmenorutile to contain from 13*74 to 19*64 per 

 cent of Cb a 6 , and one specimen showed 0*43 per cent Ta 2 6 . 

 He retains the name ilmenorutile, and it will probably stand 

 for a columbium-iron-rich rutile. Prior§ reviewed Brogger's 

 results and found that the Cb 2 6 amounted to from 33*02 to 

 33*50 per cent Cb 2 5 , but found no more Ta„0 6 . In an inde- 

 pendent analysis of an ilmenorutile from the Ilmen Mountains, 

 however, he found 21*73 per cent Cb„0 6 and 14*70 per cent 

 Ta a 3 (see table p. 442). 



The mineral from Craveggia, .Northern Piedmont, is one 

 which was first described by Zambonini| as bearing titanium, 

 zirconium, tantalum and columbium, a mistake not unnatural 

 owing to the difficulties of distinguishing in a chemical way 

 between these elements. 



After the first publication by Zambonini, further work was 

 done in collaboration with Prior and the mineral was shown to 

 carry!" no zirconium but to have the composition (mean analy- 

 sis)** indicated in column I of the table given below, with which 

 are given for comparison an analysis of ilmenorutile (No. II) 

 from the Ilmen Mountains,ff and the mineral from the Black 

 Hills (No. Ill), the analysis of which has been described. 



*Loe. cit. 



f Quoted by J. Dana, System of Mineralogy, p. 238. 



X Brogger, W. C. , Die Mineralen der sudnorwegischen Granitpegmatitgange. 

 Pt. 1, Niobate, Tantalate, Titanate and Titanniobate, p. 46. 



§ Op. cit. p. 87. 



|| Zambonini, Ferruccio, Struverite, un nouvo minerale. Rend. R. Accad. 

 Sci. Napoli, 1907, ser. 3, vol. xiii, pp. 35-44. 



IT Op. cit. ** Op. cit, p. 84. 



ft Op. cit. p. 87. 



