480 TT. E. Hidden and J. B. Mackintosft — Yttria and 



Thoro-gummite, a hydrated uranium thoro-silicate. 



This mineral, of which we have been able to gather about 

 one kilo, occurs intimately associated with fergusonite and 

 cyrtolite, and masses up to three ounces have been found, 

 though for the most part it is in very small pieces. It is 

 of a dull yellowish brown color, has hardness above that of 

 gummite, or 4-4 - 5, and occurs commonly massive, though 

 several well denned groups of zircon-shaped crystals have been 

 discovered with angles near to those of zircon. It has a char- 

 acteristic color, after ignition, becoming of a dull greenish hue, 

 thus it is distinguished from freyalite, eucrasite and thorite, 

 which species it otherwise resembles in some respects. Its 

 specific gravity varies from 4*43 to 4'54. It is easily soluble 

 in nitric acid. The analj T tical results are : 



Oxygen ratio. 



Si0 2 13-085 43-62 = 2-000 



U0 3 22-43 23-37 = 1-071 



Th0 2 41-44 31-22 ] 



A1 2 3 ... 965 2-83 | 



Fe 2 3 0-845 1-59 | 



(CeT) 2 3 . etc.. 6-69 Atomic weight = 135, 6'30 J-43 64 = 2-001 



PbO____ 2-16 0-97 ! 



CaO 0-41 0-73 J 



H 2 -. 7-88 43-78 = 2-008 



P 2 5 ... • 1-19 



Moisture 1-23 



98-325 



Regarding phosphorus as non-essential and as combined with 

 the slight excess of uranium, above that which is required by 

 the formula which we derive, and with the undetermined and 

 lost constituents, we get the oxygen ratio of U0 3 : Si0 2 : Th0 2 : 

 H a O=l :'2:2:2. The last three terms are in the proportion 

 required by thorite, and we see that the molecule of the min- 

 eral may be regarded as made up of three molecules of thorite 

 linked together by one of uranic oxide forming a compound 

 molecule, which at first sight seemingly complex, is really of 

 great simplicity. 



Using graphic notation, the formula of the mineral is 



U0 6 (ThOSi) 3 (OH) I „, or when written in the usual manner UO„ 

 STh0 2 , 3Si0 2 , 6H 3 0. The thoria and silica bear the same re- 

 lation to the uranium, and it seems better to regard the 

 mineral as a hydrated thoro-silicate of uranium, rather than as 

 a urano-silicate of thorium, or as a double silicate of uranium 

 and thorium, if indeed we might not go further and consider 

 the whole as a duo-deci-atomic molecule of a complex inorganic 



