Thoria Minerals from Llano County, Texas. 483 



We have found two distinct varieties, of which we here ap- 

 pend analyses and description. 



Fergusonite, mono-hydrated. — Specific gravity = 5 "6 7. Hard- 

 ness 6-6*5, forms tetragonal, with acute octahedral termina- 

 tions, a zirconoid plane hemihedrally developed and, rarely, the 

 basal pinacoid. The crystals are rough and dull gray exteriorly 

 but with a bronzy sub-metallic appearance on the surface of 

 fracture, which is small conchoidal and brilliant. Thin splin- 

 ters show a yellowish-brown translucence. Color bronzy hair- 

 brown. Streak and powder dull brown. It is infusible but 

 on ignition the powdered mineral changes to a pale olive-green 

 color, and a momentary glow creeps over the mass at the point 

 of redness. Fragments decrepitate violently when heated. 

 With a microscope a peculiar light brown muddiness is noticed 

 and the mineral is filled with minute streaks and spots of a 

 darker shade, all of which may indicate incipient alteration. 



Crystals often have a thin coating of, or are otherwise partly 

 altered to, the tri-hydrated variety next described. It is de- 

 composed when in fine powder by hydrochloric acid, with 

 separation of columbic acid. The analytical results are as fol- 

 lows. 



Cb 2 5 



1.. 46'27 % 







tygen ral 



10. 

 86-30 



U0 3 



1-54 







1-59 



Th0 2 



3-38 





256 "] 





Al 2 O s 



0-09 





0-27 





Fe 2 3 



0-98 



Atomic weights, 



1-83 





(A) Y 2 3 * 



... 23-95 



110-55 



26-70 





(B)Y 2 3 * ....... 



... 18-38 



113-3 



20-07 



> 52-65 



PbO 



1-43 





0-64 

 0-30 





ZnO 



0-24 





CaO 



0-10 





0-18 





MgO 



004 





o-io J 





Ignition H 2 



1-98 





11-00 N 



-15-79 



110° C. H 2 



0-04 





. ( 



F 



0-91 



Atomic ratio, 



4-79 j 







99-33 





Less = F 



0-38 









98-95 



Counting U0 3 as combined with a portion of the bases in 

 the proportion R 2 3 -U0 3 , we have for the oxygen ratio of the 

 other constituents, counting fluorine as replacing hydroxy 1, 



Cb 2 6 :R 2 8 :( H ^ ):: 86-30: 51 -06: 15-79 or 5-07:3:0-928 



This leads to the formula Cb 2 5 , E 2 3 , H 5 ; or if bases are 

 counted as EO then R 3 Cb 2 7 (OH, F) 2 . 



* Total Y 2 3 , etc., and Ce earths =42 -33. 



