124 



MINERALOGY 



Ortho series of domes, plus and minus, (hok), (hok). 



Clino series of domes, (ohk). 



Orthopinacoid, (100). 



Clinopinacoid, (010). 



Basal pinacoid, (001). 



Examples. Some of the most important rock-forming minerals 

 are members of this type, as : 



Orthoclase, KAlSi 3 O 8 . Epidote, HC^AlsSisOw. 



Augite. Gypsum, CaS0 4 , 2 H 2 O. 



Amphibole. 



Fig. 244 represents a combination of the unit prism, (110), 

 orthopinacoid, (100), clinopinacoid, (010), minus unit pyramid, 

 (111), and the plus orthodome, (101), of augite. 



CLASS, MONOCLINIC HEMIMORPHIC 

 TYPE 4, DIGONAL POLAR 



Symmetry. Crystals of this type possess one digonal axis of 

 symmetry, the b axis, Fig. 245. The forms may be considered as pro- 



o 



o 



FIG. 245. Type 4, Digonal Polar. 



FIG. 246. 



duced by a polar development of type 5, along the orthoaxis ; thus 

 the plane and center of symmetry is lost, and yielding hemi forms 

 either side of the plane of symmetry each of which may occur 

 independently, Fig. 246. 



