As may be seen from these examples, a great variety of twins may be drawn. The only serious restrictions on twins drawn with Twins are that they must all be derived from a single original individual, composition planes must pass through the center, and contact and interpenetration twins may not be intermingled. One may draw multiple interpenetration twins in which the individuals turn out to be different, but in contact twins, the composition planes are applied to all individuals, and all the individuals are exactly the same or enantiomorphic.
In the Twins option, composition planes must go through the center of the crystal, but it is certainly possible to simulate off-center contact twins with the Epitaxial Crystals option.
For moderately complicated twins, such as fivelings, sixlings, etc. in which the individuals are all identical it usually saves computer time to treat them as contact twins and use for a twin operator the pseudo-symmetry operator of the twin. On the other hand using interpenetration twins usually requires fewer twin individuals and less operator time. For very complex cases like the phillipsite twenty-fourling (example 5) it may be necessary to use interpenetration twins. In all cases it may be easier, and the results simpler and aesthetically more satisfactory (if not strictly correct), if the pseudo-symmetry of the twin aggregate is used as twin operator instead of the true twin operators.
Interpenetration twins in high-symmetry systems, especially the cubic system, can give some complex and interesting shapes, based on fairly simple forms and twin operations. Try for example the spinel law - reflection on (111) or rotation by 180 or 60 degrees on [111] - on various isometric shapes such as cubes, tetrahedra, dodecahedra, distorted octahedra (unequal tetrahedra), and general and special forms of the lower-symmetry groups of the cubic system.