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Magnetite plaquettes are naturally asymmetric materials in meteorites

Queenie H. S. Chan, Michael E. Zolensky, James E. Martinez, Akira Tsuchiyama and Akira Miyake
Magnetite plaquettes are naturally asymmetric materials in meteorites
American Mineralogist (September 2016) 101 (9): 2041-2050


Life on Earth shows preference toward the set of organics with particular spatial configurations. Enantiomeric excesses have been observed for alpha -methyl amino acids in meteorites, which suggests that chiral asymmetry might have an abiotic origin. A possible abiotic mechanism that could produce chiral asymmetry in meteoritic amino acids is their formation under the influence of asymmetric catalysts, as mineral crystallization can produce spatially asymmetric structures. Although magnetite plaquettes have been proposed to be a possible candidate for an asymmetric catalyst, based on the suggestion that they have a spiral structure, a comprehensive description of their morphology and interpretation of the mechanism associated with symmetry-breaking in biomolecules remain elusive. Here we report observations of magnetite plaquettes in carbonaceous chondrites (CC) that were made with scanning electron microscopy and synchrotron X-ray computed microtomography (SXRCT). We obtained the crystal orientation of the plaquettes using electron backscatter diffraction (EBSD) analysis. SXRCT permits visualization of the internal features of the plaquettes. It provides an unambiguous conclusion that the plaquettes are devoid of a spiral feature and, rather that they are stacks of individual magnetite disks that do not join to form a continuous spiral. Despite the lack of spiral features, our EBSD data show significant changes in crystal orientation between adjacent magnetite disks. The magnetite disks are displaced in a consistent relative direction that lead to an overall crystallographic rotational mechanism. This work offers an explicit understanding of the structures of magnetite plaquettes in CC, which provides a fundamental basis for future interpretation of the proposed symmetry-breaking mechanism.

ISSN: 0003-004X
EISSN: 1945-3027
Serial Title: American Mineralogist
Serial Volume: 101
Serial Issue: 9
Title: Magnetite plaquettes are naturally asymmetric materials in meteorites
Affiliation: NASA, Johnson Space Center, Houston, TX, United States
Pages: 2041-2050
Published: 201609
Text Language: English
Publisher: Mineralogical Society of America, Washington, DC, United States
References: 58
Accession Number: 2016-096419
Categories: Petrology of meteorites and tektites
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 2 tables
Secondary Affiliation: Jacobs Engineering, USA, United StatesKyoto University, JPN, Japan
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Abstract, copyright, Mineralogical Society of America. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 201647
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