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This Article Figures Only Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Google Scholar Articles by Kimura, M. Articles by Goresy, A. E.

Kushiroite, CaAlAlSiO₆: A new mineral of the pyroxene group from the ALH 85085 CH chondrite, and its genetic significance in refractory inclusions

¹ Faculty of Science, Ibaraki University, Bunkyo 2-1-1, Mito 310-8512, Japan
² Department of Earth and Planetary Science, Graduate School of Science, University of Tokyo, Hongo, Bunkyo-Ku, Tokyo 113-0033, Japan
³ Institute of Mineralogy, Petrology and Economic Geology, Graduate School of Science, Tohoku University, Sendai 980-8578, Japan
⁴ Bayerisches Geoinstitut, Universität Bayreuth, D-95440 Bayreuth, Germany

Correspondence: ^* E-mail: makotoki{at}mx.ibaraki.ac.jpetal.

The new mineral kushiroite, belonging to the pyroxene group, was first discovered in a refractory inclusion in the CH group carbonaceous chondrite ALH 85085. The chemical formula is Ca_1.008(Mg_0.094Fe_0.034Al_0.878)(Al_0.921Si_1.079)O₆, containing 88% CaAlAlSiO₆ and 12% diopside components. We identified the exact nature of kushiroite by micro-Raman spectroscopy and electron backscatter diffraction (EBSD) analyses. The results are consistent with those obtained from the synthetic CaAlAlSiO₆ pyroxene, thus indicating a monoclinic structure (space group C2/c). Although CaAlAlSiO₆ has been one of the most important hypothetical components of the pyroxene group, it is here for the first time established to be a naturally occurring mineral. We named this pyroxene with >50% CaAlAlSiO₆ component kushiroite, which was recently approved by the Commission on New Minerals, Nomenclature and Classification of the International Mineralogical Association (IMA2008-059). The name is for Ikuo Kushiro, Professor Emeritus at the University of Tokyo, Japan, and eminent experimental petrologist, for his outstanding experimental investigations on silicate systems involving the Ca-Tschermak component. There is no obvious evidence for impact in this inclusion. We suggest that metastable crystallization of this pyroxene took place from refractory melts in the solar nebula. Coexisting grossite-bearing refractory inclusions in the type specimen ALH 85085 show ²⁶Mg excesses with inferred initial ²⁶Al-²⁷Al ratios between 2.1 x 10^–6 to 3.9 x 10^–5, providing evidence that condensation, melting, and crystallization took place in the solar nebula when ²⁶Al was still extant.

Key Words: Kushiroite • pyroxene • Ca-Tschermak component • refractory inclusion • CH chondrite

This article has been cited by other articles:

				C. Ma, S. B. Simon, G. R. Rossman, and L. Grossman Calcium Tschermak's pyroxene, CaAlAlSiO6, from the Allende and Murray meteorites: EBSD and micro-Raman characterizations American Mineralogist, October 1, 2009; 94(10): 1483 - 1486. [Abstract] [Full Text] [PDF]