Wychoff — Crystal Structure of Alabandite. 247 



chloride arrangement,'^ (II), then the observed low 

 degree of symmetry must be ascribed to some sort 

 of a lack of symmetry in the shape of the fields of force 

 about the atoms of manganese or of sulphur or of both. 

 If the low degree of symmetry is in this instance to be 

 accounted for by the arrangement of the atoms and if 

 the symmetry is really that of the tetrahedral class 





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Fig. 3. — A possible arrangement for the atoms of alabandite. The posi- 

 tions of the manganese and sulphur atoms can be but slightly displaced, how- 

 ever, from the positions which they occupy in the grouping of figure 2. This 

 arrangement is a possible one only if the symmetry of alabandite is 

 tetartohedral. 



(hemimorphic.hemihedry), then grouping (I) with values 

 of u and u' such that there is but slight departure from 

 the ^^ sodium chloride arrangement ' ' would be in agree- 

 ment with the existing information ; if, on the other hand, 

 the symmetry is tetartohedral, a similar arrangement 

 based upon (IV) would be possible. The definite elimi- 

 nation of this last possibility could be effected if a careful 

 crystallographic investigation showed the crystal to be 



