•Table number 2 735 



Polar axis 3-fold — Trigonal Pyramidal Class or (Trigonal Pyramidal- 

 Hemimorpliic ) Group, Hexagonal (Trigonal) System. 



Polar axis 2-fold — Monoclinic Sphenoidal Class or Hemimorpliic 

 Group, Monoclinic System. 



Polar axis 1-fold — Triclinic Asymmetric Class or Asymmetric Group, 

 Triclinic System. 

 (&) Opposite ends of crystals like (axis not polar). (Symmetry by rota- 

 tion about a singular axis, then by reflection in a plane per- 

 pendicular to the axis of rotation) — Amehaxial Order. 



With a singular 3-fold axis — Trigonal Rhombohedral Class or Tri- 

 rhombohedral Group, Hexagonal (Trigonal) System. 



With a singular 2-fold axis — Tetragonal Bisphenoidal Class or Tetar- 

 tohedral Group, Tetragonal System. 



With only 1-fold axes — Triclinic Pinacoidal Class or Normal Group, 

 Triclinic System. 



2. With more than one axis having a period greater than one-fold: 



(With one vertical axis and two or more lateral axes perpendicular to it. 



The lateral axes may join the mid-points of opposite edges) — 



Polyaxial Order, 

 (a) With one or more singular axes. 



With one singular 6-fold axis — Hexagonal Trapezohedral Class or 



Trapezohedral Group, Hexagonal System. 

 With one singular 4-fold axis — Tetragonal Trapezohedral Class or 



Trapezohedral Group, Tetragonal System. 

 With one singular 3-fold axis — Trigonal Trapezohedral Class or 



Trapezohedral Group, Hexagonal (Trigonal) System. 

 With three singular 2-fold axes perpendicular to each other — Ortho- 

 rhombic Bisphenoidal Class or Sphenoidal Group, Orthorhombic 



System. 

 (&) With no singular axis, but with three like axes perpendicular to 



each other ; also with four like 3-fold axes — Sometimes one set, 



sometimes the other is more prominent. 

 The like perpendicular axes 4-fold — Pentagonal Icositetrahedral Class 



or Plagihedral Group, Isometric System. 

 The like perpendicular axes 2-fold — Tetrahedral Pentagonal Dodeca- 



hedral Class or Tetartohedral Group, Isometric System. 



B. WITH ONE OR MORE PLANES OF SYMMETRY 



1. With no or hut one axis of symmetry having a period greater than one-fold: 

 (a) Opposite ends of crystals unlike (axis polar) and the plane or planes 



of symmetry passing through the polar axis — Hedral Order. 

 Polar axis 6-fold — Dihexagonal Pyramidal Class or Hemimorphic 



Group, Hexagonal System. 

 Polar axis 4-fold — Ditetragonal Pyramidal Class or Hemimorphic 



Group, Tetragonal System. 

 Polar axis 3-fold — ^Ditrigonal Pyramidal Class or Rhombohedral 



Hemimorphic Group, Hexagonal (Trigonal) System. 

 Polar axis 2-fold — Orthorhombic Pyramidal Class or Hemimorphic 



Group, Orthorhombic System. 



