Quick Search:    advanced search

GSW Home   GeoRef Home   My GSW Alerts   Contact GSW   About GSW   Journals List   Help

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 Ma, C. Articles by Grossman, L.

Calcium Tschermak’s pyroxene, CaAlAlSiO₆, from the Allende and Murray meteorites: EBSD and micro-Raman characterizations

¹ Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California 91125, U.S.A.
² Department of the Geophysical Sciences, University of Chicago, Chicago, Illinois 60637, U.S.A.
³ Enrico Fermi Institute, University of Chicago, Chicago, Illinois 60637, U.S.A.

Correspondence: ^* E-mail: chi{at}gps.caltech.edu

Calcium Tschermak’s pyroxene (CaTs), CaAlAlSiO₆, is well known as an important component in pyroxene. It is a member of the Ca clinopyroxene group in which Al dominates in the M1 site. Pyroxenes with more than 80 mol% CaTs were observed previously in Ca-,Al-rich refractory inclusions (CAI) from five carbonaceous chondrites. This study re-investigated the near end-member CaTs in the Allende and Murray chondrites. Electron backscatter diffraction (EBSD) is used to establish that its crystal structure is monoclinic, C2/c; a = 9.609 Å, b = 8.652 Å, c = 5.274 Å, β =106.06°, V = 421.35 ų, and Z = 4. Its EBSD pattern is an excellent match to that of synthetic CaAlAlSiO₆ with the C2/c structure. MicroRaman is also carried out to confirm the crystal structure. The Allende CaTs, with 46.00 wt% Al₂O₃ and 97 mol% Al in the M1 site, has the formula Ca_1.02(Al_0.97Fe_0.01Mg_0.01)_0.99(Si_1.00Al_1.00)_2.00O₆. It occurs as micrometer-sized crystals along with melilite, hibonite, perovskite, spinel, corundum, Ti³⁺-rich pyroxene, and grossular in a fluffy Type A CAI. It is probably a secondary phase resulting from the alteration of gehlenitic melilite. The CaTs in Murray, with a formula Ca_0.98(Al_0.81Mg_0.16Ti_0.04⁴⁺)_1.01(Si_1.11Al_0.89)_2.00O₆, occurs with hibonite and Al-rich diopside in a glass-free refractory spherule. This sample formed by solidification of a once-molten droplet early in the history of the solar system.

Key Words: Calcium Tschermak’s pyroxene • CaTs • CaAlAlSiO₆ • Al-rich pyroxene • refractory inclusion • Allende meteorite • Murray meteorite • carbonaceous chondrite

This article has been cited by other articles:

				C. Ma and G. R. Rossman Grossmanite, CaTi3+AlSiO6, a new pyroxene from the Allende meteorite American Mineralogist, October 1, 2009; 94(10): 1491 - 1494. [Abstract] [Full Text] [PDF]