Thoria Minerals from Llano County, Texas. 479 



Regarding the loss by ignition as non-essential, the oxy- 

 gen ratio of all the bases to silica is exactly 3 : 4, which 

 leads to the formula R 2 3 , 2Si0 2 , in which R 2 3 may be 

 replaced by its equivalent in RO, R0 2 or R0 3 . There is no 

 simple ratio between the sesquioxide and other bases. This 

 mineral, therefore, differs from gadolinite in containing twice 

 as much silica. It has other points of difference, viz : it con- 

 tains no glucina, which has been regarded as a characteristic 

 constituent of gadolinite, and there is a very large preponder- 

 ance of sesquioxides among the bases. For comparison we 

 append two analyses of gadolinite from this locality by Genth* 

 and Eakins. f 



Genth. 



Si0 2 22-80 



Th0 2 



MnO 0-18 



FeO 12-93 



G-10 9-19 



CaO 0-71 



MgO 0-11 



K 2 0-12 



JSTaoO 0-23 



A1 2 3 0-31 



Fe 2 3 



Ce 2 3 2-66 



(DiLa) 2 3 . 5-01 



(Y,Er) 2 3 . 44-45 



H 2 0-79 



P 2 5 .... 



Insoluble.. 0-93 



Gadolinite, Llano Co., Texas. 



Sp. G. = 4-254 | Kakins. 



Oxygen ratio. 



76-00 



0-25 1 

 17-96 

 36-61 I 



1-27 }- 56-86 "] 



0'27 



0-13 I 



0-37 J }- 116-11 



0-90 \ 



2-46 J-59'25 J 

 4-59 | 

 51-30 J 



100-42 



Sp. G. = 4-239§ 

 Oxygen ratio. 



23-79 

 0-58 

 trace 

 12-42 

 11-33 

 0-74 



• traces 



0-96 

 2-62 

 5-22 

 41-55 

 1-03 

 0-05 



100-29 



0-44 1 



79-30 



17-25 



45-18 



1-32 



1-63-75 



K21-13 



1 

 1-80 J 



2-43 [-56-94 J 



4-77 | 1 

 47-94 j |1 



Regarding the water and phosphoric acid as accidental and 

 using the molecular weight for the yttria earths determined 

 by Eakins (260) for the calculation of Genth's analysis, we get 

 the oxygen ratio of all the bases to silica of 3*055 : 2 and 

 3'054 : 2 respectively, giving the general formula R 2 3 , Si0 2 in 

 which R 2 3 may be replaced by its equivalent in RO and R0 2 . 

 Both of these analyses seem to show a tendency towards an 

 equality of the sesquioxides to the monoxides, though there is 

 a preponderance of sesquioxides in the one and of protoxides 

 in the other. They differ also from our analysis of yttrialite 

 in the" small percentage of thoria, which in the latter amounts 

 to one-eighth of the total bases in equivalency. 



* F. A. Genth, this Journal, September, 1889. 



f L. G. Eakins, private communication from Professor F. W. Clarke. 



i Molecular weight = 260. § At 17° C. 



|| Bidymium spectrum very strong. ^f Erbium spectrum weak. 



