Ma, Chi and Simon, Steven B. and Rossman, George R. and Grossman, Lawrence (2009) Calcium Tschermak’s pyroxene, CaAlAlSiO_6, from the Allende and Murray meteorites: EBSD and micro-Raman characterizations. American Mineralogist, 94 (10). pp. 1483-1486. ISSN 0003-004X http://resolver.caltech.edu/CaltechAUTHORS:20100107-142329782
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Calcium Tschermak’s pyroxene (CaTs), CaAlAlSiO_6, 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 Å^3, and Z = 4. Its EBSD pattern is an excellent match to that of synthetic CaAlAlSiO_6 with the C2/c structure. MicroRaman is also carried out to confirm the crystal structure. The Allende CaTs, with 46.00 wt% Al_(2)O_3 and 97 mol% Al in the M1 site, has the formula Ca_(1.02)(Al_(0.97)Fe_(0.01)Mg_(0.01))0.99(Si_(1.00)Al_(1.00))_(Σ2.00)O_6. It occurs as micrometer-sized crystals along with melilite, hibonite, perovskite, spinel, corundum, Ti^(3+)-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_(0.81)Mg_(0.16)Ti_(0.04)^(4+))_(Σ1.01)(Si_(1.11)Al_(0.89))_(Σ2.00)O_6, 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.
|Additional Information:||© 2009 Mineralogical Society of America. Manuscript received March 3, 2009; manuscript accepted March 23, 2009; manuscript handled by Bryan Chakoumakos.|
|Subject Keywords:||Calcium Tschermak’s pyroxene; CaTs; CaAlAlSiO_6; Al-rich pyroxene; refractory inclusion; Allende meteorite; Murray meteorite; carbonaceous chondrite|
|Official Citation:||Ma, Chi, Simon, Steven B., Rossman, George R., Grossman, Lawrence Calcium Tschermak's pyroxene, CaAlAlSiO6, from the Allende and Murray meteorites: EBSD and micro-Raman characterizations American Mineralogist 2009 94: 1483-1486|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Jason Perez|
|Deposited On:||11 Jan 2010 22:39|
|Last Modified:||26 Dec 2012 11:40|
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