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Northwest Africa 11917
Basic information Name: Northwest Africa 11917
     This is an OFFICIAL meteorite name.
Abbreviation: NWA 11917
Observed fall: No
Year found: 2012
Country: (Northwest Africa)
Mass:help 304 g
Classification
  history:
Recommended:  Winonaite    [explanation]

This is 1 of 35 approved meteorites classified as Winonaite.   [show all]
Search for other: Primitive achondrites, Winonaites
Comments: Approved 15 Sep 2018
Writeuphelp
Writeup from MB 107:

Northwest Africa 11917 (NWA 11917)

(Northwest Africa)

Purchased: 2012

Classification: Primitive achondrite (Winonaite)

Petrography: No chondrules are present, but there are irregularly shaped silicate clusters (50-700 µm in size) that may have been derived from recrystallized chondrule fragments. There is no clear igneous texture. Olivine exhibits mildy undulose extinction. Plagioclase also occurs. The rock contains ~20 vol.% metal plus sulfide. Opaque phases include kamacite, martensite, taenite, schreibersite, ferroan alabandite, and magnesiochromite. Metal and sulfide grains average ~100 µm in size. There are some grains of polycrystalline troilite and polycrystalline kamacite. There are rare 8x12-µm-size patches of daubreelite at the ede of some troilite grains. There are also rare ~40-µm-size metal grains with martensitic structure, rimmed by cloudy taenite. There is a single thick, elongated band of troilite at the edge of one thin section (~300 × 3000 µm).

Geochemistry: Also present are plagioclase (Ab84.7±0.2Or2.7±0.2; n=5); kamacite (in wt.%): 92.5 Fe, 0.48 Co, 0.06 P, 6.8 Ni, <0.03 Si; taenite: 73.5 Fe, 0.17 Co, <0.03 P, 23.5 Ni, <0.03 Si; troilite: 62.6 Fe, 37.0 S, 0.35 Cr; magnesiochromite: 67.3 Cr2O3, 5.8 MnO, 12.0 MgO, 6.2 FeO. The O-isotopic composition of replicate samples was analyzed by R. Greenwood (OU): δ17O = 1.876±0.006, δ18O = 4.541±0.011, Δ17O = -0.486±0.012 (per mil); this is in the winonaite range.

Classification: This is one of the most reduced winonaites, with very little FeO in the mafic silicates. The presence of some grains of polymict troilite and kamacite indicates moderately high shock, but the mildly undulose extinction in the olivine (characteristic of S2) suggests that the rock was shocked and then annealed, and perhaps (mildly) shocked again.

Data from:
  MB107
  Table 0
  Line 0:
Place of purchase:Tucson, Arizona
Date:P 2012
Mass (g):304.3
Pieces:1
Class:Winonaite
Shock stage:S2
Weathering grade:W1
Fayalite (mol%):0.72±0.44 (n=6)
Ferrosilite (mol%):0.53±0.21 (n=15)
Wollastonite (mol%):1.3±0.3
Classifier:A. Rubin, UCLA
Type spec mass (g):20.73
Type spec location:UCLA
Main mass:Brad Kern
Comments:Submitted by Alan Rubin
Plots: O isotopes:  
Institutions
   and collections
OU: Planetary and Space Sciences Department of Physical Sciences The Open University Walton Hall Milton Keynes MK7 6AA United Kingdom, United Kingdom (institutional address; updated 8 Dec 2011)
UCLA: Institute of Geophysics and Planetary Physics, University of California, Los Angeles, CA 90095-1567, United States (institutional address; updated 17 Oct 2011)
Catalogs:
References: Published in Meteoritical Bulletin, no. 107, in preparation (2018)
Find references in NASA ADS:
Find references in Google Scholar:
Geography: 
Coordinates:Unknown.

Statistics:
     This is 1 of 6877 approved meteorites from (Northwest Africa) (plus 2037 unapproved names)

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