GUIDE TO THE MIXERALOGIC COLLECTIONS 



19 



hedron of the normal group similar to that of the tetrahedron 

 to the octahedron. 



Fig. 56 



Fig. 51 



Two other forms, the tetragonal tris tetrahedron (fig. 58) and 

 the hexakistetrahedron (fig. 59) are occasionally found in combi- 

 nation. Some combinations in this group are shown in fig. 60-65. 



Fig. 58 



Fig. 68 



Fig. 60 



Fig. 61 



Fig. 62 



Fig 6i 



Fig. 64 



Fig. 65 



