110 



MINERALOGY 



Hexagonal prism first order, KT (hoho). 

 Base, (0001). 



Examples. Quartz, Si0 2 , crystallizes in this type, of which 

 Fig. 210 is a combination of the hexagonal prism, first order, plus 



FIG. 210. Right-handed 

 Quartz : Combination of 

 m(10TO), r(10ll), z(OlTl), 

 ), x(5161). 



FIG. 211. Left-handed 

 Quartz, m(ioro), r(lOTl), 

 z(OlTl), s(2lfl), x(65Tl). 



and minus rhombohedrons, first order, plus trigonal pyramid, and 

 the right plus trigonal trapezohedron, a right-hand crystal. Fig. 

 211 is a left-hand crystal. Cinnabar, HgS, also belongs here. 



CLASS, TRIGONAL HEMIMORPHIC 

 TYPE 9, TRIGONAL POLAR 



Symmetry. Crystals of this type 

 possess one axis of trigonal sym- 

 metry, the c axis, Fig. 212. The type 

 is. a polar development of the trigonal 

 equatorial, in which the hemitrigonal 

 pyramids may occur independently, 

 yielding two new forms. 



o 



FIG. 212. Type 9, Trigonal 

 Polar. 



f n 



na : : a : me 



n i 



Forms 



I. Trigonal hemipyramids of the 

 third order, 



; (hkli), (ma), (ikhi), (iEki), (hkii), 



(khil), (ikhl), (ihkl). 



