International
Tables for
Crystallography
Volume A
Space-group symmetry
Edited by M. I. Aroyo

International Tables for Crystallography (2016). Vol. A, ch. 3.2, p. 740

Table 3.2.2.3 

H. Klappera and Th. Hahna

Table 3.2.2.3| top | pdf |
Categories of crystal systems distinguished according to the different forms of the indicatrix

Crystal systemShape of indicatrixOptical character
Cubic Sphere Isotropic (not doubly refracting)
[\!\left.\matrix{\hbox{Tetragonal}\hfill\cr \hbox{Trigonal}\hfill\cr \hbox{Hexagonal}\hfill\cr}\right\}\hfill] Rotation ellipsoid [\!\left.\matrix{\hbox{Uniaxial}\hfill\cr \noalign{\vskip 2pt}\cr \hfill\cr \hbox{Biaxial}\hfill\cr}\right\}\matrix{\hbox{Anisotropic}\hfill\cr\quad\hbox{(doubly}\hfill\cr\quad\hbox{refracting)}\hfill\cr}]
[\!\left.\matrix{\hbox{Orthorhombic}\hfill\cr\hbox{Monoclinic}\hfill\cr\hbox{Triclinic}\hfill\cr}\right\}] General ellipsoid