FORMS OF CRYSTALLIZATION. 



37 



Examples 



EIQIIT SQUABE Paisn. 



RIGHT SQUARE-BASED OCTAHEDRON. 



FIG. 28. 



FIG. 29. 



FIG. 30. 



3. Eight prismatic system (right rhomboidal or rectan- 

 gular prismatic system), in which the three axes are of un- 

 equal length, though at right angles. 



4. Oblique prismatic system, which 

 includes the right rhomboidal prism 

 and the oblique rhombic prism. The 

 three axes may be of unequal length 

 while two are at right angles, and the 

 vertical axis inclined to one of these. 



Example Fig. 30. 



5. Double oblique prismatic system in which three axes 

 are unequal, and not any at right angles. 



6. Rhombohedral system (regular hexagonal 

 system). There are four axes, three of which 

 are in the same plane and inclined to one 

 another at an angle of 60, the other being 

 vertical : frequently the prism is capped by a 

 six-sided pyramid. 



Example Fig. 31. 



Various names are given to the above systems, viz. : 



1. Cubic, regular system, monometric. 



2. Square prismatic, tetragonal, quadratic, dime trie. 



3. Right prismatic, rhombic, trimetric. 



4. Monoclinic. 



5. Triclinic or anorthic. 



6. Rhombohedral. 



Crystalline form is not always sufficient evidence to rely 

 upon in the determination of a mineral, as several different 



FIG. 31. 



