Structure analysis and conditions of formation of akimotoite in the Tenham chondrite
- Creators
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Tschauner, O.
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Ma, C.
- Prescher, C.
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Prakapenka, V. B.
Abstract
Akimotoite (Mg,Fe)SiO_3 is one of the most common mineralogical indicators for high-level shock metamorphism in meteorites. First described 1997, its occurrence has been amply confirmed in a number of highly shocked chondrites. Yet, a thorough structure analysis of natural akimotoite has remained extant. Here we report accurate cell parameters, fractional atomic coordinates, and site occupancies for natural akimotoite from the holotype specimen based on synchrotron microdiffraction. The variation of unit cell shape and volume with Fe content define mixing volumes. Based on the mixing volume relation for akimotoite and hemleyite, we constrain the unit cell volume of endmember hemleyite to 273.8 ± 1.0 Å^3. We show that mixing is nearly ideal for low Fe content but evolves to positive excess volume toward the Fe endmember. Based on this finding and the actual composition of akimotoite in Tenham, we show that this mineral has formed by solid–solid transformation prograde from enstatite, not by crystallization from melt.
Additional Information
© 2017 The Authors. Meteoritics & Planetary Science published by Wiley Periodicals, Inc. on behalf of The Meteoritical Society. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited. Received 13 July 2017; revision accepted 12 October 2017. This project was supported in part through NNSA contractual agreement DE-NA0001974. Diffraction data were collected at GeoSoilEnviroCARS, which is supported by the National Science Foundation-Earth Sciences (EAR-1634415) and Department of Energy-GeoSciences (DE-FG02-94ER14466). This research used resources of the Advanced Photon Source, a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357. SEM, EBSD, and EPMA analyses were carried out at the Caltech GPS Division Analytical Facility, which is supported, in part, by NSF Grants EAR-0318518 and DMR-0080065. We thank associate editor Dieter Stöffler and reviewers Ming Chen, Haozhe Liu, and Dongzhou Zhang for their helpful comments.Attached Files
Published - Tschauner_et_al-2018-Meteoritics___Planetary_Science.pdf
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Additional details
- Eprint ID
- 83869
- DOI
- 10.1111/maps.13009
- Resolver ID
- CaltechAUTHORS:20171213-095137348
- DE-NA0001974
- Department of Energy (DOE)
- EAR-1634415
- NSF
- DE-FG02-94ER14466
- Department of Energy (DOE)
- DE-AC02-06CH11357
- Department of Energy (DOE)
- EAR-0318518
- NSF
- DMR-0080065
- NSF
- Created
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2017-12-13Created from EPrint's datestamp field
- Updated
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2021-11-15Created from EPrint's last_modified field