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MINERALOGY 



CLASS, DIHEXAGONAL HEMIMORPHIC 



TYPE 18, DIHEXAGONAL POLAR 



Symmetry. By a polar development of the holohedral forms 

 of type 20, all the symmetry lying in the equatorial plane is lost, 



leaving the dihexagonal axis and the 

 six vertical planes intersecting in the c 

 axis as the symmetry of this type, 

 Fig. 168. 



Forms. The new forms would be, 

 upper and lower dihexagonal hemi- 

 pyramids, Fig. 169. Also upper and 

 lower hexagonal hemipyramids of the 

 first and second orders, Fig. 170. 



Possible forms to be found in com- 

 bination on crystals of this type would 

 be: 



FIG. 168. Type 18, Dihexag- 

 onal Polar. 



Upper and lower dihexagonal hemipyramid, 



u/1 



na: 



: a : me 



n i 



; (hktl), (hkU). 



Upper and lower hemipyramid of the second order, 



FIG. 169. The Upper Dihex- 

 agonal Hemipyramid, (hkil.) 



FIG. 170. The Upper Hex- 

 agonal Hemipyramid of 

 the First Order, (hofil). 



u/1 



Upper and lower hemipyramid of 

 a: co a : a: me N 



the first order, 



; (hohl), (hohl). 



Dihexagonal prism, na: 



n i 



:a:ooc; (hkio). 



Hexagonal prism of the first order, a:ooa:a:ooc; (1010) 

 Hexagonal prism of the second order, 2 a : 2 a : a : oo c ; (1120). 



