Twin Operator
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Dialog Box: Twin Operator [ Twins Dialog]

<Standard Mode - see also Twin Operator (Cartesian)>.

A twin operator may be either reflection on a rational plane or rotation on a rational vector. Normal twins according to the system commonly used for feldspars should be entered as reflection twins, giving the indices of the composition or twin plane. For parallel twins enter the indices of the twin axis is the twin operator.

For rotation twins, the rotation angle is normally an integral fraction of 360 degrees. A rotation angle is not needed for reflections twins - the angle will be set automatically to 180.

Note that composition planes must always be entered separately, even if the twin is by reflection.

Parent twin. With SHAPE V6.1.2, twins may be derived from other twins, not just the main crystal. This should simplify entry of many multiple twins. All twins must still be identical, and have a common center point at the origin (see the Lamellar Albite Twins example for methods of doing lamellar twins which do not have a common center).

Note that the number required here is the twin operator number, which is 0 for the main crystal, 1 for the first twin, and so on. After calculation, the crystals are numbered 1 for the main crystal, 2 for the first twin, and so on - if you click with the mouse on a crystal, you will get the crystal number, not the twin operator number.