Twinning

Abstract

In Section 1.3.1, general terms with reference to twinning are explained. Subsequently, the terms `twin lattice' and `twin index' are defined and illustrated by several examples in Section 1.3.2 and the implication of twinning on the reflection pattern in reciprocal space is discussed in Section 1.3.3. Twinning by merohedry and by pseudo-merohedry is described in Section 1.3.4. For each combination of point group and Bravais lattice, the possible twin operations for twins by merohedry are given in Table 1.3.4.1. Table 1.3.4.2 shows the simulated Laue classes, the extinction symbols, the simulated `possible space groups' and the possible true space groups for crystals twinned by merohedry. For cases in which the twin element cannot be recognized by direct inspection, a procedure for the calculation of the twin element is described in Section 1.3.5. This chapter is also available as HTML from the International Tables Online site hosted by the IUCr.