126 



MINERALOGY 



CLASS, DOMATIC HEMIHEDRONS 

 TYPE 3, EQUATORIAL 



Symmetry. Crystals of this type possess a plane of symmetry 

 only, Fig. 251. They may be considered as hemihedrons formed 



FIG. 251. Type 3, Equatorial. 



FIG. 252. 



by selecting pairs of faces of type 5, which meet in the equatorial 

 plane, as the shaded faces of the minus pyramid of Fig. 252. 



Forms 



I. Upper and lower plus and minus hemipyramids of each 

 series of 



K(hkl), 



two faces each, (- ~)u/l, K(hkl), K(hkl), 



K(hkl), Fig. 253. 



II. Front and 



| rear hemiprisms of 



two faces each, 



K(hko), K(hko). 

 Fig. 254. 



III. Upper and 

 lower clinodomes, 

 & : nb : mc 



FIG. 253. The Lower Minus 

 Hemipyramid. 



K(ohl), (ohl), Fig. 

 255, of two faces 

 each. 



IV. Upper and lower, back and front 



FIG. 254. Front 

 Hemiprism. 



