Natural quasicrystal with decagonal symmetry

Abstract

We report the first occurrence of a natural quasicrystal with decagonal symmetry. The quasicrystal, with composition Al[subscript 71]Ni[subscript 24]Fe[subscript 5], was discovered in the Khatyrka meteorite, a recently described CV3 carbonaceous chondrite. Icosahedrite, Al[subscript 63]Cu[subscript 24]Fe[subscript 13], the first natural quasicrystal to be identified, was found in the same meteorite. The new quasicrystal was found associated with steinhardtite (Al[subscript 38]Ni[subscript 32]Fe[subscript 30]), Fe-poor steinhardtite (Al[subscript 50]Ni[subscript 40]Fe[subscript 10]), Al-bearing trevorite (NiFe[subscript 2]O[subscript 4]) and Al-bearing taenite (FeNi). Laboratory studies of decagonal Al[subscript 71]Ni[subscript 24]Fe[subscript 5] 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.