Evidence of cross-cutting and redox reaction in Khatyrka meteorite reveals metallic-Al minerals formed in outer space

Abstract

We report on a fragment of the quasicrystal-bearing CV3 carbonaceous chondrite Khatyrka recovered from fine-grained, clay-rich sediments in the Koryak Mountains, Chukotka (Russia). We show higher melting-point silicate glass cross-cutting lower melting-point Al-Cu-Fe alloys, as well as unambiguous evidence of a reduction-oxidation reaction history between Al-Cu-Fe alloys and silicate melt. The redox reactions involve reduction of FeO and SiO2 to Fe and Fe-Si metal, and oxidation of metallic Al to Al2O3, occurring where silicate melt was in contact with Al-Cu-Fe alloys. In the reaction zone, there are metallic Fe and Fe-Si beads, aluminous spinel rinds on the Al-Cu-Fe alloys, and Al2O3 enrichment in the silicate melt surrounding the alloys. From this and other evidence, we demonstrate that Khatyrka must have experienced at least two distinct events: first, an event as early as 4.564 Ga in which the first Al-Cu-Fe alloys formed; and, second, a more recent impact-induced shock in space that led to transformations of and reactions between the alloys and the meteorite matrix. The new evidence firmly establishes that the Al-Cu-Fe alloys (including quasicrystals) formed in outer space in a complex, multi-stage process.

Previously unknown quasicrystal periodic approximant found in space

“…1) clearly attached to the meteorite fragment (dark areas in the upper panel of Fig. 1), as typically observed for other fragments of the Khatyrka meteorite 4,7,13,14 . Detailed examination by scanning electron microscopy, single-crystal X-ray diffraction, micro-computed tomography and transmission electron microscopy of fragments from Grain 126 associated to proxidecagonite revealed the presence of trevorite, diopside, forsterite, ahrensite, clinoenstatite, nepheline, coesite, stishovite, pentlandite, Cu-bearing troilite, icosahedrite, khatyrkite, taenite, Al-bearing taenite, steinhardtite, decagonite, hollisterite, stolperite and kryachkoite 4,5,7,13,15–17 .…”

“…1), as typically observed for other fragments of the Khatyrka meteorite 4,7,13,14 . Detailed examination by scanning electron microscopy, single-crystal X-ray diffraction, micro-computed tomography and transmission electron microscopy of fragments from Grain 126 associated to proxidecagonite revealed the presence of trevorite, diopside, forsterite, ahrensite, clinoenstatite, nepheline, coesite, stishovite, pentlandite, Cu-bearing troilite, icosahedrite, khatyrkite, taenite, Al-bearing taenite, steinhardtite, decagonite, hollisterite, stolperite and kryachkoite 4,5,7,13,15–17 . The recovery of different Al-Ni-Fe crystalline (steinhardtite) and QC (decagonite) intermetallic phases, motivated a careful search for other metallic fragments, which led to the discovery of a particle with composition close to that of the known Al-Ni-Fe decagonal QC but with different diffraction characteristics.

Figure 1Micro-computed tomographic images (at different orientations) of the entire grain (labeled number 126).

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“…All recovered fragments of Khatyrka including Grain 126 have been shown to include non-metallic minerals with CV3-like oxygen isotopic compositions 4,7,13,14 confirming their common meteoritic origin. The Khatyrka meteorite formed 4.5 billion years ago during the earliest stages of the solar system and contains evidence of a heterogeneous distribution of pressures and temperatures during impact shock, in which some portions of the meteorite reached at least 5–10 GPa and 1200–1500 °C.…”

Icosahedral Quasicrystal Layer Observed on λ Phase in Al-Cu-Fe Alloy

“…Further out, there are five points related to 3-fold rotational axes arranged in a similar way, forming a larger pentagon. Such relative arrangement of the rotational axes is consistent with IQC structure and previous reports[17] [18], proving clearly that the extra layer is of IQC structure, different from the substrate λ phase.Further, the result of elemental mapping supports this conclusion. The columnlike structure has been identified as λ-phase (or ω-phase) with chemical formulaof Al 13 Fe 4 [4] [5] or Al 7 Cu 2 Fe [19] [20] in previous reports.…”

Structure of Cubic Al73.8Pd13.6Fe12.6 Phase with High Al Content

“…The Al-Cu-Fe and Al-Pd-Mn QCs have been extensively studied due to their stability, unique structural model, and potential industrial applications, such as wear-resistant coatings [6][7][8][9][10]. The formation, phase stability, and structure of Al-Cu-Fe QCs have been notably studied since the first natural QCs discovered in the Al-Cu-Fe system a decade ago [11][12][13][14][15][16][17][18][19][20][21]. Meanwhile, a variety of Al-based complex metallic phases have been synthesized and analyzed as their chemical compositions and crystal structures are quite similar to their quasicrystal counterparts [22][23][24][25][26].…”