GUIDE TO THE MIXERALOGIC COLLECTIOXS 



17 



Pyritohedron. The pyritohedron (fig. 46, 47, model 4) is named 

 from the species pyrite, of which it is a characteristic form. 



Fig. 46 



Fig. 47 



It is composed of 12 pentagonal faces, each of which is par- 

 allel to one axis and meets the other two at unequal distances. 

 As will be seen from fig. 46 and 47 the pyritohedron exists in 

 complementary forms, fig. 46 being known as the plus and fig. 

 47 as the minus form. The 24 faces of the plus and minus 

 pyiitohedrons have the same position in space as the 24 faces 

 of the corresponding tetrahexahedron of the normal group. 

 Diploid. The diploid (fig. 48, 49) is composed of 24 quadrilat- 



Fig. 48 



Fig. 49 



Fig. 50 



- 51 Fig. 52 



era! faces each of which meets the axes ;ii unequal distances. 

 The complementary plus (fig. 18) and minus (fig. 49) forms bear 

 the same relation to the hexoctahedron of the normal group 



