THE COMPOSITION OF YTTRIAL1TE. WITH A CRITICISM OF THE 
FORMULA ASSIGNED TO THALfMTE. 
By W. F. HlLLEBRAND. 
In a paper describing the new yttrium silicate thalenite," the author, 
C. Benedicks, casts doubt on the formula assigned by Hidden and 
Mackintosh* to their mineral yttrialite from Llano County, Tex., for 
which they deduced the formula R 2 0. 5 2Si0 2 or R 2 Si 2 7 , in which R 2 3 
includes the sesquioxide equivalents of very considerable percentages 
of monoxides and dioxides. Benedicks would assign yttrialite to a 
group of which rowlandite is the prototype and to which he believes 
thalenite and kainosite belong, these being either plain basic salts of 
H 6 Si 2 7 of the type R"K/" 4 Si 4 15 or derivatives in which the fifteenth 
xy gen atom is replaced by its equivalent in fluorine (rowlandite) or 
X) 3 (kainosite), as shown below. 
YeeS10 7 =Y\ 
H 2 < >0 
Y = Si 2 7 = Y/ 
Y = Si 2 Q 7 = Y x 
Fe< >0 
Y = Si 2 7 = Y/ 
Y = 8i 2 7 = Y-Fl 
Fe< 
Y = Si 2 7 = Y-Fl 
Ca = Si 2 7 = Y 
H 4 < 
Ca=Si 2 7 = Y 
Thalenite. 
Yttrialite. 
Rowlandite. 
CO, Kainosite. 
Benedicks says: 
Dem Yttrialit, von Hidden and Mackintosh beschrieben, sollte die Formel R 2 :! , 
5i0 2 zukommen, worin R hauptsachlich Ytter- und Thorerde ist. Dabei wird aber 
i. 4% Eisenoxydul in der Analyse vernachlassigt. Wird dies nebst etwas Kalk und 
|leioxyd mitgerechnet, so bekommt man die Formel Fe // 0, 2R 2 :! , 4Si( >.,, analog 
lit der des Thalenits, welche besser die Zusanimensetzung des Yttrialits wiedergibt, 
deich die Ubereinstimmung gar nicht gut ist. 
a Bull. Geol. Inst, Upsala, 4, 1898, 1. 
&Am. Jour. Sci., ser. 3, vol. 38, 1889, p. 477. 
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