From Crystals to Quasicrystals: There’s Plenty of Room Between Them

Beside the three natural quasicrystals, icosahedrite (Bindi et al. in Science 324:1306–1309, 2009; Bindi et al. in Am Mineral 96:928–931, 2011), decagonite (Bindi et al. in Sci Rep 5:9111, 2015a; Bindi et al. in Am Mineral 100:2340–2343, 2015b) and the new unnamed icosahedral phase (i-phase II) with composition Al61Cu32Fe7 (Bindi et al. in Sci Rep 6:38117, 2016), we discovered the first natural periodic approximant to the decagonal quasicrystal, Al71Ni24Fe5. The approximant, with chemical formula Al34Ni9Fe2, does not correspond to any previously recognized synthetic (Lemmerz et al. in Philos Mag Lett 69:141–146, 1994) or natural phase. The mineral was named proxidecagonite, derived from “periodic approximant of decagonite” (from the truncated Latin word proxǐmus followed by the name of the quasicrystalline mineral decagonite).