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Si Isotopes of BrownleeiteBrownleeite is a manganese silicide, ideally stoichiometric MnSi, not previously observed in nature until its discovery within an interplanetary dust particle (IDP) that likely originated from a comet [1]. Three discrete brownleeite grains in the IDP L2055 I3 (4 microns in size, hereafter IDP I3) were identified with maximum dimensions of 100, 250 and 600 nm and fully analyzed using scanning-transmission electron microscopy (STEM) [1]. One of the grains (100 nm in size) was poikilitically enclosed by low-Fe, Mn-enriched (LIME) olivine. LIME olivine is epitaxial to the brownleeite with the brownleeite (200) parallel to the olivine c* [1]. LIME olivine is an enigmatic phase first reported from chondritic porous IDPs and some unequilibrated ordinary chondrites [ 2], that is commonly observed in chondritic-porous IDPs. Recently, LIME olivine has been also found in comet Wild-2 (Stardust) samples [3], indicating that LIME olivine is a common mineral component of comets. LIME olivine has been proposed to form as a high temperature condensate in the protosolar nebula [2]. Brownleeite grains also likely formed as high-temperature condensates either in the early Solar System or in the outflow of an evolved star or supernova explosion [1]. The isotopic composition of the brownleeite grains may strongly constrain their ultimate source. To test this hypothesis, we performed isotopic analyses of the brownleeite and the associated LIME olivine, using the NASA/JSC NanoSIMS 50L ion microprobe.
Document ID
20100009378
Document Type
Other
Authors
Nakamura-Messenger, K. (NASA Johnson Space Center Houston, TX, United States)
Messenger, Scott R. (NASA Johnson Space Center Houston, TX, United States)
Ito, M. (NASA Johnson Space Center Houston, TX, United States)
Keller, L. P. (NASA Johnson Space Center Houston, TX, United States)
Clemett, S. J. (NASA Johnson Space Center Houston, TX, United States)
Jones, J. H. (NASA Johnson Space Center Houston, TX, United States)
Tatsuoka, H. (Roentgenanalytik Messtechnik G.m.b.H Taunsstein, Germany)
Zolensky, M. E. (NASA Johnson Space Center Houston, TX, United States)
Tatsuoka, H. (Shizuoka Univ. Japan)
Date Acquired
August 25, 2013
Publication Date
March 1, 2010
Subject Category
Geophysics
Report/Patent Number
JSC-CN-19666
Meeting Information
Lunar and Planetary Science Conference(The Woodlands, TX)
Distribution Limits
Public
Copyright
Public Use Permitted.

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