As discussed in Chapter 2, quasicrystals are an unusual form of matter with orderly, but nonperiodic atomic arrangements. They can display diffraction patterns with otherwise forbidden rotational symmetry, e.g., fivefold, eightfold, and higher axes of symmetry (Levine and Steinhardt 1984; Shechtman et al. 1984). Princeton physicist Paul Steinhardt spent decades searching for natural quasicrystals, a quest documented in his book, The Second Kind of Impossible (Steinhardt 2019).