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Examples of Ee planes.

All glide planes parallel to two axes in space groups Fmm2, Fmmm, $Fm\bar 3$, $Fm\bar 3m$and $Fm\bar 3c$ (Nos. 42, 69, 202, 225 and 226), as well as certain planes in the five space groups listed in §3.

Diagonally oriented Ee planes occur in space groups I4mm, I4cm, $I\bar 42m$, I4/mmm, I4/mcm, $I\bar 43m$and $Im\bar 3m$ (Nos. 107, 108, 121, 139, 140, 217 and 229).

In ITA83 all these Ee planes are drawn rather arbitrarily as either dotted or dashed lines in their parallel projections. Fig. 4 shows the diagram of space group I4cm (No. 108), both as shown in ITA83 and with use of the new symbol.

 

Fig. 4. (a) Diagram of space group I4cm (No. 108) taken from ITA83. (b) Same, modified by using the graphical symbol proposed in § 2, for the parallel projection of an Ee plane.

Although Ek is a new print symbol, in the diagrams of ITA83 all glide planes Ek have been drawn satisfactorily with the same conventions as used for Ea/b/c glide planes. As in these cases, there is a single special glide vector (perpendicular to the crystal axis in net N, cf. Table 3). When this vector is, for instance, parallel to the plane of projection, the Ek plane is always drawn as the dashed line prescribed by the relevant convention. Therefore, no new graphical symbol is proposed for Ek glide planes.

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