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ssss1 (a) Mirror plane (m) with the translation vector (t), contrasted with (b) a glide plane (g) with the translation vector (t/2) combined with mirror reflection.
4.2.2 Compound symmetry operations
Glide reflection
Rotoinversion
Screw rotationa
Source: Wenk and Bulakh (2004). © Cambridge University Press.
4.3 TWO‐DIMENSIONAL MOTIFS AND LATTICES (MESHES)
The symmetry of three‐dimensional crystals can be quite complex. Understanding symmetry in two dimensions provides an excellent basis for understanding the increased complexity that characterizes three‐dimensional symmetries. It also provides a basis for learning to visualize planes of constituents within three‐dimensional crystals. Being able to visualize and reference lattice planes is of the utmost importance in describing cleavage and crystal faces and in the identification of minerals by X‐ray diffraction methods.
4.3.1 Plane point groups
ten plane point groups1, 2, 3, 4, 6, m, 2mm, 3m, 4mm, and 6mm