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A new mineral with an olivine structure and pyroxene composition in the shock-induced melt veins of Tenham L6 chondrite

Xie Zhidong, Thomas G. Sharp, Kurt Leinenweber, Paul S. DeCarli and Przemek Dera
A new mineral with an olivine structure and pyroxene composition in the shock-induced melt veins of Tenham L6 chondrite
American Mineralogist (February 2011) 96 (2-3): 430-436

Abstract

We report a new mineral that occurs in shock-induced melt veins of the Tenham L6 chondrite. The new mineral, identified by transmission electron microscopy (TEM), occurs as acicular nanocrystals in a glassy matrix at the edge of shock-induced melt veins that crystallized during rapid quench at high pressure. The elongate crystals have aspect ratios up to 25. Widths range from approximately 5 to approximately 40 nm and lengths are up to 500 nm. Energy-dispersive X-ray spectroscopy (EDS) analyses provide the relative cation abundances that are consistent with a pyroxene-like stoichiometry: Na (sub 0.06) Ca (sub 0.02) Mg (sub 0.71) Fe (sub 0.20) Al (sub 0.11) Si (sub 0.94) O (sub 3) . Selected area electron diffraction (SAED) patterns from single-crystal and polycrystalline aggregates indicate an olivine structure with refined cell parameters: a=4.78, b=10.11, and c=5.94 Aa and a calculated density of 3.32 g/cm (super 3) . Synchrotron X-ray microdiffraction data are consistent with an olivine structure and provide similar cell parameters: a=4.778, b=10.267, c=5.937 Aa. The pyroxene composition represents a large deviation from olivine stoichiometry, (Na (sub 0.08) Ca (sub 0.03) Mg (sub 0.95) Fe (sub 0.26) Al (sub 0.15) Si (sub 0.25) [] (sub 0.28) ) (sub 2) Si (sub 1) O (sub 4) , with 0.28 formula units of vacancies ([]), 0.11 of Na (super +) plus Ca (super 2+) , and 0.25 of Si (super 4+) , in octahedral sites. Our observations indicate that a metastable and nonstoichiometric olivine structure can crystallize from a silicate melt during rapid quench. Trace amounts of such defects may be present in stable olivines in the deep upper mantle.


ISSN: 0003-004X
EISSN: 1945-3027
Coden: AMMIAY
Serial Title: American Mineralogist
Serial Volume: 96
Serial Issue: 2-3
Title: A new mineral with an olivine structure and pyroxene composition in the shock-induced melt veins of Tenham L6 chondrite
Affiliation: Nanjing University, School of Earth Sciences and Engineering, Nanjing, China
Pages: 430-436
Published: 201102
Text Language: English
Publisher: Mineralogical Society of America, Washington, DC, United States
References: 47
Accession Number: 2011-026537
Categories: Mineralogy of silicatesPetrology of meteorites and tektites
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 2 tables
Secondary Affiliation: Arizona State University, USA, United StatesSRI International, USA, United StatesUniversity of Chicago, USA, United States
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: 201115
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