152 W. F. Hillebrand — Composition of Yttrialite. 



My excuse for such a lengthy publication on a matter still 

 unsettled is the desire to prevent general acquiescence in the 

 grouping under one type of minerals which can by no means 

 be regarded as proven to belong to that type, and to which 

 yttrialite certainly does not belong. 



Summary. 



The empirical formula of Hidden and Mackintosh for yttrialite 

 is confirmed, and it is shown that the basic formula of Bene- 

 dicks rests on error and has no standing. 



The formula of Hidden and Mackintosh is not, however, sus- 

 ceptible of representation as a simple salt of the acid H 6 Si 2 7 . 

 On the purely hypothetical assumption of admixture of anhy- 

 drous thorite, the remaining constituents afford ratios conform 

 ing quite closely to those of a basic metasilicate R // E /// 3 (E, /// 0)' 8 

 (SiO s ), 



It is shown for two reasons fully discussed that the formula 

 proposed by Benedicks for thalenite is to be regarded as doubt- 

 ful. 



Laboratory U. S. G-eol Survey, 



Washington, D. C, Nov. 19th, 1901. 



