Results of Crystal Analysis. 

 The spacings of the four faces are in the relation : 

 d m : d m : d m : d m = l : T409 : 1-043 : 0468, 



507 



Fig. 1. 

 Xenotime 









1 





(101) 









_1_ 





(110) 







1 





(III) 





1 



1 





^(100) 



or approximately 



\A+0V*+© 2 * 



(la) 



If for a moment we do not take into consideration the 

 oxygen atoms, but only the Y and P atoms, the lattice would 

 give the following relation : 



9 A 



d m \: d no : d m : d m = l : ^/2 : j= ==: j= ==.. (15) 



\MfJV°+ey 



We see that the relations (la) and (lb) are the same 

 except for the face (111), where the spacing observed is 

 only i of the value to be expected from the lattice. 



The question is now, whether the oxygen atoms might 

 be arranged in such a way as to make the three first 

 maxima of the (111) face disappear or become vanishingly 

 small. 



2M2 



