Abstract
We report the first occurrence of a natural quasicrystal with decagonal symmetry. The quasicrystal, with composition Al71Ni24Fe5, was discovered in the Khatyrka meteorite, a recently described CV3 carbonaceous chondrite. Icosahedrite, Al63Cu24Fe13, the first natural quasicrystal to be identified, was found in the same meteorite. The new quasicrystal was found associated with steinhardtite (Al38Ni32Fe30), Fe-poor steinhardtite (Al50Ni40Fe10), Al-bearing trevorite (NiFe2O4) and Al-bearing taenite (FeNi). Laboratory studies of decagonal Al71Ni24Fe5 have shown that it is stable over a narrow range of temperatures, 1120 K to 1200 K at standard pressure, providing support for our earlier conclusion that the Khatyrka meteorite reached heterogeneous high temperatures [1100 < T(K) ≤ 1500] and then rapidly cooled after being heated during an impact-induced shock that occurred in outer space 4.5 Gya. The occurrences of metallic Al alloyed with Cu, Ni, and Fe raises new questions regarding conditions that can be achieved in the early solar nebula.
Highlights
We report the first occurrence of a natural quasicrystal with decagonal symmetry
Laboratory studies of decagonal Al71Ni24Fe5 have shown that it is stable over a narrow range of temperatures, 1120 K to 1200 K at standard pressure, providing support for our earlier conclusion that the Khatyrka meteorite reached heterogeneous high temperatures [1100, T(K) # 1500] and rapidly cooled after being heated during an impact-induced shock that occurred in outer space 4.5 Gya
Detailed examination by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) of tiny particles from Grain 126 revealed the presence of Al-bearing trevorite, coesite, stishovite, magnetite, diopside, forsterite, clinoenstatite, sodalite, nepheline, pentlandite, Cu-bearing troilite, icosahedrite, khatyrkite, cupalite, taenite, Albearing taenite, and the recently approved mineral steinhardtite[17]
Summary
We report the first occurrence of a natural quasicrystal with decagonal symmetry. The quasicrystal, with composition Al71Ni24Fe5, was discovered in the Khatyrka meteorite, a recently described CV3 carbonaceous chondrite. A decagonal phase in the AlNi-Fe system was first synthesized, again by rapid solidification, in 1989 by Tsai et al.[12] Lemmerz et al.[13] later www.nature.com/scientificreports identified the stability range to be centered around composition Al71Ni24Fe5 – consistent with the composition of the natural quasicrystal – over a narrow range of temperatures between 1120 K and 1200 K This supports our earlier conclusion[8] that the Khatyrka meteorite reached heterogeneous high temperatures and rapidly quenched after undergoing an impact-induced shock that occurred in outer space at the beginning of the solar system. 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
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