axe de symétrie d'ordre n

CONT: Un axe de symétrie est dit axe d'ordre n par rapport à une surface ou à un système de plan, et, en minéralogie, par rapport à une face, quand cet axe de symétrie est tel qu'en faisant tourner la figure de 2 [pi]/n, on retombe sur la surface primitive.

CONT: ""Symmetry classes"". Every crystal belongs to one of the 32 different classes of symmetry, or point groups. The standard notation for describing these classes is that of Schoenflies, who assigned symbols to the various possible symmetry elements according to the following rules: Symbol: C[subscript n]. Symmetry Element Possessed by Group: n-fold axis. ... Symbol: T (tetrahedral). Symmetry Element Possessed by Group: four three-fold axes towards vertices or regular tetrahedron. Symbol: O. Symmetry Element Possessed By Group: three mutually perpendicular four-fold axes (cubic group).
OBS: symmetry"": In general, a figure or expression is said to be symmetric if parts of it may be interchanged without changing the whole. ... A right circular cone has an axis of symmetry. A geometric figure has n-fold rotational symmetry about an axis if a rotation of 360°/n is a symmetry of the figure. Thus an axis of symmetry can be a rotational axis. For example, an axis through the centre of a square perpendicular to the plane is a 4-fold axis since a rotation of 360°/4 produces an identical figure; a diagonal is a 2-fold axis.