Impact-induced shock and the formation of natural quasicrystals in the early solar system

Abstract

The discovery of a natural quasicrystal, icosahedrite (Al_(63)Cu_(24)Fe_(13)), accompanied by khatyrkite (CuAl_2) and cupalite (CuAl) in the CV3 carbonaceous chondrite Khatyrka has posed a mystery as to what extraterrestrial processes led to the formation and preservation of these metal alloys. Here we present a range of evidence, including the discovery of high-pressure phases never observed before in a CV3 chondrite, indicating that an impact shock generated a heterogeneous distribution of pressures and temperatures in which some portions reached at least 5 GPa and 1,200 °C. The conditions were sufficient to melt Al–Cu-bearing minerals, which then rapidly solidified into icosahedrite and other Al–Cu metal phases. The meteorite also contains heretofore unobserved phases of iron–nickel and iron sulphide with substantial amounts of Al and Cu. The presence of these phases in Khatyrka provides further proof that the Al–Cu alloys are natural products of unusual processes that occurred in the early solar system.

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