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A closed form composed of six faces of which three faces at the top alternate with three 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.
An open form made up of two parallel faces
2-fold axis or bar 1
A single face comprising of a form
An open form consisting of two nonparallel faces symmetrical with respect to a mirror plan (m)
Two nonparallel faces symmetrical with respect to a 2-fold axis
An open form composed of 3,4,5,6,8, or 12 faces, all of which are parallel two the same axis. Except for certain " " in the monoclinic system, the axis is one of the crystallographic axes
An open form composed of 3,4,6,8, or 12 nonparallel faces that meet at a point
A closed form consisting of two upper faces that alternate with two lower faces, off-set by 90 degrees
A closed form with 8 or 12 faces grouped in symmetrical pairs. In the tetragonal version of this form, pairs of upper faces are related by an axis of four-fold rotoinversion to pairs of lower faces. The 12 faces of the hexagonal version of this 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 developed example of this form, each face is a scalene triangle