The the

As dihedral [ dieːdər ] ( dihedron , Greek for "Zweiflächner") is a regular polygon (triangle, quadrilateral, etc.) is referred to, the front and rear sides has. In the series of polyhedra it is therefore the simplest, flat special case.

The expression is used within group theory as a dihedral group and in the description of two- surface angles, which are referred to as dihedral angles .

In crystallography , non-closed forms are called that consist of two surfaces with a common edge. These forms are called doma ( Greek δῶμα "house") when the two surfaces are mirrored, or sphenoid (from Greek σφήν "wedge") when they are transformed into one another by a twofold axis of rotation. The doma is the general surface form (and namesake) of the monoclinic- domatic crystal class ( m ), the sphenoid that of the monoclinic-sphenoidal class ( 2 ).

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  Monoclinic Dieder: Sphenoid (left) and Doma (right)

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  Dihedral angle as the angle between two planes

literature

• Hans-Joachim Bautsch , Will Kleber , Joachim Bohm : Introduction to crystallography . Oldenbourg Wissenschaftsverlag, 1998 ( limited preview in Google book search).