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(i) The graphical symbols and their explanations (columns 2 and 3) are independent of the projection direction and the labelling of the basis vectors. They are, therefore, applicable to any projection diagram of a space group. The printed symbols of glide planes (column 4), however, may change with a change of the basis vectors, as shown by the following example.
In the rhombohedral space groups (161) and (167), the dotted line refers to a c glide when described with `hexagonal axes' and projected along [001]; for a description with `rhombohedral axes' and projection along [111], the same dotted glide plane would be called n. The dash-dotted n glide in the hexagonal description becomes an a, b or c glide in the rhombohedral description; cf. the first footnote
in Section 1.3.1.
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(ii) The graphical symbols for glide planes in column 2 are not only used for the glide planes defined in Chapter 1.3
, but also for the further glide planes g which are mentioned in Section 1.3.2
(Note x
) and listed in Table 4.3.2.1
; they are explained in Sections 2.2.9
and 11.1.2
.
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(iii) In monoclinic space groups, the `parallel' glide vector of a glide plane may be along a lattice translation vector which is inclined to the projection plane.
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(iv) In 1992, the International Union of Crystallography introduced the `double' glide plane e and the graphical symbol ..--..-- for e glide planes oriented `normal' and `inclined' to the plane of projection (de Wolff et al., 1992 ); for details of e glide planes see Chapter 1.3
. Note that the graphical symbol for e glide planes oriented `parallel' to the projection plane has already been used in IT (1935) and IT (1952) .
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