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

Zhidong Xie, Thomas Sharp, Kurt Leinenweber, Paul S. DeCarli, Przemek Dera

Research output: Contribution to journalArticle

4 Scopus citations

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 ∼5 to ∼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: Na0.06Ca 0.02Mg0.71Fe0.20Al0.11 Si 0.94O3. 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 Å and a calculated density of 3.32 g/cm3. 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 A. The pyroxene composition represents a large deviation from olivine stoichiometry, (Na 0.08Ca0.03Mg0.95 Fe0.26Al 0.15Si0.250.28)2Si 1O4, with 0.28 formula units of vacancies (□), 0.11 of Na+ plus Ca2+, and 0.25 of Si4+, 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.

Original languageEnglish (US)
Pages (from-to)430-436
Number of pages7
JournalAmerican Mineralogist
Volume96
Issue number2-3
DOIs
StatePublished - Feb 1 2011

Keywords

  • Melt vein
  • Olivine
  • Shock-induced
  • Tenham

ASJC Scopus subject areas

  • Geophysics
  • Geochemistry and Petrology

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