Читать книгу Earth Materials - John O'Brien - Страница 89

Symmetry operations may be simple or compound. Simple symmetry operations produce repetition of a unit of pattern or motif using a single type of operation. Compound symmetry operations involve motif repetition using a combination of two symmetry operations. Simple symmetry operations, discussed in this section, include (1) translation, by specific distances in specified directions, (2) rotation, about a specified set of axes, (3) reflection, across a mirror plane, and (4) inversion, through a point called a center. These operations are discussed below and provide useful insights into the geometry of crystal structures and the three‐dimensional properties of such crystals.