An open form consisting of two nonparallel faces symmetrical with respect to a mirror plan (m) (3)
Two nonparallel faces symmetrical with respect to a 2-fold axis (4)
An open form composed of 3,4,5,6,8, or 12 faces, all of which a are parallel tow the same axis. Except for certain prisms in the monoclinic system, the axis is one of the crystallographic axes (5-11)
An open form composed of 3,4,6,8, or 12 nonparallel faces that meet at a point (12-18)
A closed form with 8 or 12 faces grouped in symmetrical pairs. In the tetragonal scalenohedron, pairs of upper faces are related by an axis of four-fold rotoinversion to pairs of lower faces. The 12 faces of the hexagonal scalenohedron display three pairs of upper faces and three pairs of lower faces in alternating positions. The pairs are related by a center of symmetry, wichis is part of a 3-fold rotoinversion, bar 3. In an ideally develped scalenohedron, each face is a scalenen triangle
A closed form composed of six faces of which three faces at the top alternate with threee at the bottom, the two sets of faces being offset by 60 degrees.
Are only found in point groups of bar3 2/m, 3 2, and bar 3.
A closed form consisting of two upper faces that alternate with two lower faces, off-set by 90 degrees