I Hi: MONOCLINIC SYSTEM 



121 



IK i longer divide space into eight equal octants, but into octants of 

 two (lilTcrent sixes, four of which are large, or obtuse, and four 

 smaller, or acute. The two upper front and the two lower back 

 octants an- large and designated octants; the smaller are the -f 

 octants. As the inclination of ft to d varies with the substance, 

 the angle between these two axes, measured in the + octants is 

 designated by ft, and is therefore less than 90, which added to the 



o / 



two axial ratios - and - make three crystalline characters for the 

 b b 



cm. 



CLASS, HOLOHEDRAL (HOLOSYMMETRIC) 

 TYPE 5, DIGONAL EQUATORIAL 



Symmetry. Crystals of this type possess one digonal axis, 

 the b axis ; one plane of symmetry, the equatorial plane, at right 



angles to the c axis and 

 containing ft and c, and 

 a center. Figure 238 

 represents the relation 

 of the axes and plane 

 of symmetry, and also 

 the general position of 



the monoclinic crystals 

 IK 



? in relation to the ob- 



FIG. 238. The Monoclinic Axes and Plane of 

 Symmetry. 



server. Fig. 239 representing the 



symmetry of the type, it differs from 



others in that the b axis and not c is 



perpendicular to the plane of the 



paper. In viewing a crystal of this 



type held in the general position, the equatorial plane will be 



vertical. 



FIQ. 239. Type o, Digonal Equa- 

 torial. 



