The first and, until now, the only known natural quasicrystal, Al 63 Cu 24 Fe 13 (icosahedrite), exhibits icosahedral symmetry and was reported in 2009 as grains within a rock sample found in the Museo di Storia Naturale of the Università degli Studi di Firenze (catalog number 46407/G), labeled as khatyrkite and identified as coming from the Khatyrka ultramafic zone in the Koryak Mountains in far eastern Russia1,2,3. This sample contains a metallic core consisting primarily of icosahedrite, khatyrkite (CuAl 2 ), cupalite (CuAl) and β-phase (AlCuFe) intergrown with diopside, forsterite and minute amounts of stishovite. The core is encased in a white rind that includes spinel, pyroxene ranging in composition from diopside to hedenbergite, nepheline and sodalite. The composition of icosahedrite was found to closely match that of the first stable quasicrystal synthesized in the laboratory4.

The rock sample was subsequently shown to be a fragment of the Khatyrka meteorite, an oxidized subgroup (Allende-like) CV3 carbonaceous chondrite (CV3 CC), which formed at least 4.5 billion years ago5. Additional samples of the Khatyrka meteorite were recovered in an expedition to the Koryak Mountains in Chukotka in 20116,7. A study of those samples provided clear evidence that the meteorite was subjected to a high-pressure shock and that the shock produced a heterogeneous distribution of high pressure and temperature followed by rapid cooling8. Studies of the recovered samples continue to reveal information about the mineral phases and the assemblages that resulted from the impact.

This paper reports the discovery of a second natural quasicrystal. The quasicrystal was identified in a powder sample from Grain 126 of the same Khatyrka meteorite, as described by Hollister et al.8 The quasicrystal has composition Al 71 Ni 24 Fe 5 and is the first known natural quasicrystal with decagonal symmetry, a periodic stacking of layers containing quasiperiodic atomic arrangements with ten-fold symmetry. The first decagonal quasicrystal was synthesized in the laboratory in 1985 in rapidly quenched Al-Mn samples9,10,11. A decagonal phase in the Al-Ni-Fe system was first synthesized, again by rapid solidification, in 1989 by Tsai et al.12 Lemmerz et al.13 later identified the stability range to be centered around composition Al 71 Ni 24 Fe 5 – consistent with the composition of the natural quasicrystal – over a narrow range of temperatures between 1120 K and 1200 K. This supports our earlier conclusion8 that the Khatyrka meteorite reached heterogeneous high temperatures and then rapidly quenched after undergoing an impact-induced shock that occurred in outer space at the beginning of the solar system.

Quasicrystals14,15 are novel phases of matter easily recognized by their quasiperiodic atomic arrangements (i.e., described by a sum of two or more periodic functions whose periods have an irrational ratio) and by their rotational symmetries forbidden to periodic crystals, including five-fold and ten-fold symmetry axes. More than one hundred different compositions of quasicrystals have since been synthesized in the laboratory16, many of which including metallic Al. Until now, though, Khatyrka is the only meteorite found to contain phases with metallic Al as an essential component. The existence of icosahedrite and the decagonal quasicrystal with metallic Al imply that remarkably low oxygen fugacities were achieved during the formation of the meteorite in the early solar system.