100 



MINERALOGY 



Forms 

 I. Hexagonal hemipyramid of the third order, 



u/l 



na: 



a : a : me 



n i 



;. (hkil), (khil), (hkil), (khil). 



The upper or lower half of the pyramid of the third order may 

 occur independently, Fig. 188. 



Other forms are the same as in type 18. The possible forms to 

 combine in this type will be 



Plus and minus upper and plus and minus lower hemipyramids 

 of the third order, (hkil), (khil), (hkil), (khil). 



o ! 



O ; 



FIG. 187. Type 14, Hexagonal 

 Polar. 



FIG. 188. The Upper Hexagonal 

 Hemipyramid of the Third Order. 



Upper and lower hemipyramid of the first order, (hkil), (hkil). 

 Upper and lower hemipyramid of the second order, (hh2hl), 

 (hh2hl). 



Plus and minus hexagonal prism of the third order, (hkio), 

 (khio). 



Hexagonal prism of the first order, (1010). 

 Hexagonal prism of the second order, (1120). 



Hexagonal base, upper and lower, (0001), 

 (OOOT). 



Examples. Crystals in this type are 

 rare and the hemipyramid of the third 

 order, which is the only form characteristic 

 of the type, does not occur on any min- 

 eral, but from the symmetry of the etch- 

 ing figures, nephelite, 



s 



FIG. 189. Combination of , i u i ui i 



P (iori),p(ion,m(ioTo), P laced here ' as are also the double sul ~ 

 c(oooi), c'(oooi). phate of the alkali metals, potassium and 





