Читать книгу Crystallography and Crystal Defects - Anthony Kelly - Страница 39

In some crystal classes the possibility exists of crystals being found in either a right‐handed or a left‐handed modification with the two not being superposable, in the sense that the right hand of the body cannot be superposed upon the left hand. This occurs if the crystal only possesses simple rotation symmetry operations; that is, no symmetry operation of the second kind. Therefore, mirror planes and rotoinversion axes of any degree do not appear in such crystal classes. There are 11 of these classes: 1, 2, 3, 4, 6, 23, 222, 32, 422, 622 and 432.