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Disordered chromite in the Martian meteorite Allan Hills 84001 (Articolo in rivista)

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Disordered chromite in the Martian meteorite Allan Hills 84001 (Articolo in rivista) (literal)

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Gunnlaugsson, HP; Koch, CB; Bharuth-Ram, K; Dietrich, M; Helgason, O; Madsen, MB; Mantovan, R; Naidoo, D; Steinthorsson, S; Vistisen, L; Weyer, G (2008)
Disordered chromite in the Martian meteorite Allan Hills 84001
in Hyperfine interactions
(literal)

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Gunnlaugsson, HP; Koch, CB; Bharuth-Ram, K; Dietrich, M; Helgason, O; Madsen, MB; Mantovan, R; Naidoo, D; Steinthorsson, S; Vistisen, L; Weyer, G (literal)

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\"[Gunnlaugsson, H. P.; Weyer, G.] Aarhus Univ, Dept Phys & Astron, DK-8000 Aarhus C, Denmark; [Koch, C. Bender] Univ Copenhagen, Dept Nat Sci, Fac Life Sci, DK-1871 Frederiksberg, Denmark; [Bharuth-Ram, K.] Univ KwaZulu Natal, Sch Pure & Appl Phys, ZA-4041 Durban, South Africa; [Dietrich, M.] CERN, Div EP, CH-1211 Geneva 23, Switzerland; [Helgason, O.; Steinthorsson, S.] Univ Iceland, Inst Sci, IS-107 Reykjavik, Iceland; [Madsen, M. B.; Vistisen, L.] Univ Copenhagen, Niels Bohr Inst, DK-2100 Copenhagen, Denmark; [Mantovan, R.] Lab Nazl MDM CNR INFM, I-20041 Agrate Brianza, MI, Italy; [Naidoo, D.] Univ Witwatersrand, Sch Phys, ZA-2050 Wits, South Africa (literal)

Titolo

Abstract

At room temperature the Fe-57 Mossbauer spectrum of chromite particles separated from the Martian meteorite Allan Hills 84001 is different from the Mossbauer spectrum of natural chromite. One hypothesis for this discrepancy is that the chromite in Allan Hills 84001 is found in a disordered or even amorphous state, possibly caused by a shock event. As a test of this hypothesis, we have attempted to amorphize natural chromite by ion implantation. Fe-57 emission Mossbauer spectra of chromite implanted with radioactive precursor Mn-57 ions have been measured. The spectra can be analyzed in terms of two contributions, a crystalline chromite fraction and a disordered fraction, attributed to disordered iron-chromium oxide or amorphous zones created by the implantation process. The Mossbauer parameters of the amorphous fraction are indistinguishable from those deduced from the spectrum of the chromite separate from Allan Hills 84001. A shock event is a likely explanation for these findings and with appropriate energy calibration this may possibly be used to estimate the intensity of the shock event that once modified minerals in the meteorite Allan Hills 84001. (literal)

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