Figure 2
Phys. Rev. Lett. 53, 1951 (1984)

Ten-fold way. Quasiperiodic patterns have small repeating elements but on a larger scale do not exactly repeat (top). Daniel Schechtman’s electron diffraction pattern from a metal alloy shows spots with a ten-fold rotational symmetry, which researchers in 1984 thought was impossible for a crystal (bottom). Today researchers call the material a quasicrystal because its structure is quasiperiodic.