“Ten fold??? There can be no such creature.” It was with these words that Daniel Shechtman, 2011 Nobel Laureate in Chemistry, greeted the discovery of electron diffraction patterns that violated some of the fundamental laws of crystallography. The diffraction patterns had been collected from a crystal of an alloy of aluminium and manganese that had been rapidly cooled. The fact that the samples diffracted indicated they were crystalline, but the resulting symmetry — five- and ten-fold icosahedral — was impossible, according to the well-established rules of crystallography.

Credit: © AP PHOTO/ARIEL SCHALIT; © ERIC HELLER/SPL

With his initially sceptical colleagues, Shechtman published the findings some two years after the initial observations, stating that they had “observed a metallic solid [...] with long-range orientational order, but with icosahedral point group symmetry, which is inconsistent with lattice transitions” (Phys. Rev. Lett. 53, 1951–1953; 1984). It is safe to say that reaction to the paper was mixed. On one side, some mathematicians and even crystallographers had been inspired to consider five-fold symmetry by the quasiperiodic tilings developed by Roger Penrose in the 1970s. Indeed, only six weeks after Shechtman and colleagues' paper was published, a theoretical explanation of quasicrystals — as they became to be known — was published by Paul Steinhard and Dov Levine (Phys. Rev. Lett. 53, 2477–2480; 1984).

On the opposite side of the argument was Linus Pauling, who remained convinced that there was indeed 'no such creature' and argued that the observed phenomenon could be attributed solely to symmetrically intergrown crystals, known as twins. Such scepticism has dwindled in the face of overwhelming evidence and quasicrystals have since been found in nature (Science 324, 1306–1309; 2009), as well as in re-written crystallography textbooks.