248 Wyckojf — Crystal Structure of Alahandite. 



tetrahedral.^ This seems never to have been done and 

 the author does not have at his disposal material upon 

 which to make such a study. The three possible struc- 

 tures for alabandite are shown in figures 2, 3 and 4. 



Alabandite is usually classed in the same group with 

 zinc blende.^^ This determination of its crystal struc- 

 ture, however, definitely indicates that it is in no way 







\ y 

 \ y 





f 



y 





, V y^ 



'■-/^"v,^ 



>// 



/ / 





\ 



w 



y. 



\ 





f" 



m 





--^ 



y 



\ ~\ 





\, 







y 



^^ 





#.. 



/ 



• 



y 



y 



-,^^ \ 





;>^ 







/ \, 





y' 



/^ 





y^ \ 



y 





® MANGANESE 



• 3ULPHUR. 



Fig. 4. — The last of the three possible structures for alabandite. In this 

 case also the positions of the manganese and sulphur_ atoms can differ but 

 slightly from those of figure 2. 



isomorphous mth the zinc sulphide. In this connection 

 it is of interest to note that alabandite does not have the 

 dodecahedral cleavage of zinc blende but rather the cubic 

 cleavage of the (from the standpoint of its crystal struc- 

 ture) similarly arranged sodium chloride and magnesium 

 oxide. 



* The proof that the crystal was actually tetartohedral would not in a 

 corresponding manner eliminate (I) since it is a special case of T^ as well 

 as of Tf, '\ 



" Dana, System of Mineralogy, 6th Edition, p. 59. 



