68 CONTRIBUTIONS TO MINERALOGY. [bull. 263 
SUMMARY. 
The empirical formula of Hidden and Mackintosh for yttrialite i 
confirmed, and it is shown that the basic formula of Benedicks rest: 
on error and has no standing. 
The formula of Hidden and Mackintosh is not, however, susceptibli 
of representation as a simple salt of the acid H 6 Si 2 7 . On the pure! 
hypothetical assumption of admixture of anhydrous thorite, the remain 
ing constituents afford ratios conforming quite closely to those of i 
basic metasilicate WR'" 9 (R" f Oy 9 (SiO s ) r 
It is shown for two reasons fully discussed that the formula propose( 
by Benedicks for thalenite is to be regarded as doubtful. 
