symmetry element (elemento de simetría)

Contexto del término Figure 6.2 is an illustration of a crystal of gypsum. The right-hand half of the crystal can be brought into coincidence with the left-hand half through a reflection in the hatched plane, which will equally bring the left-hand side into coincidence with the right. Every point in the crystal will be moved by this reflection operation except those which actually lie on the reflection plane itself. The plane containing these points is thus the symmetry element corresponding to the symmetry operation of reflection; it is called a mirror plane.