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Northwest Africa 7257
Basic information Name: Northwest Africa 7257
     This is an OFFICIAL meteorite name.
Abbreviation: NWA 7257
Observed fall: No
Year found: 2012
Country: (Northwest Africa)
Mass:help 180 g
Meteoritical Bulletin:  MB 100  (2012)  Martian (shergottite) 
Recommended:  Martian (shergottite)    [explanation]

This is 1 of 324 approved meteorites (plus 2 unapproved names) classified as Martian (shergottite).   [show all]
Search for other: Martian meteorites
Comments: Approved 29 May 2012
Writeup from MB 100:

Northwest Africa 7257 (NWA 7257)

(Northwest Africa)

Purchased: 2012 January

Classification: Martian meteorite (Shergottite)

History: Purchased by David Gregory in January 2012 from a Moroccan dealer at the Tucson Gem and Mineral Show.

Physical characteristics: A single, fresh gray stone (180 g) partially coated by light-brown weathering products. The medium-grained interior is dominated by randomly oriented elongate prismatic pyroxene grains and ~25 vol.% sparkling maskelynite.

Petrography: (A. Irving and S. Kuehner, UWS): Medium grained (pyroxene up to 6 mm long by 0.8 mm wide, plagioclase up to 2.5 mm long by 0.7 mm wide), with an intersertal texture. Prismatic grains of twinned and complexly-zoned clinopyroxene are accompanied by squat laths of maskelynite and accessory ilmenite, Cr-bearing ulvöspinel, pyrrhotite, chlorapatite, merrillite and rare fayalite. Regions of K-rich mesostasis are composed of microlites in partly devitrified brownish glass. Melt inclusions within pyroxene (surrounded by radial microcracks) are rich in K and P, and contain rare daughter crystals of hercynite.

Geochemistry: Pigeonite (Fs29.8-34.3Wo15.3-13.3, Fe/Mn=29-33), subcalcic augite (Fs21.1-38.9Wo32.4-29.1, Fe/Mn=26-34), ferropigeonite rims (Fs44.6-54.1Wo11.4-18.0, Fe/Mn=33-37), plagioclase (An44.0-45.1Or2.2-2.7). Oxygen isotopes (R. Tanaka, OkaU): analyses of acid-washed subsamples by laser fluorination gave, respectively δ17O 2.83, 2.85; δ18O 4.82, 4.74; Δ17O 0.294, 0.352 per mil.

Classification: Achondrite (Martian, shergottite).

Specimens: 20.1 g of type material and one polished thin section are on deposit at UWS. The main mass is held by  DGregory.

Data from:
  Table 1
  Line 1700:
Place of purchase:Tucson
Date:P 2012 January
Mass (g):180
Class:Martian (shergottite)
Shock stage:moderate
Weathering grade:low
Ferrosilite (mol%):20.2; 21.1-48.7
Wollastonite (mol%):12.4; 32.4-12.6
Classifier:A. Irving and S. Kuehner, UWS
Type spec mass (g):20.1
Type spec location:UWS
Main mass:DGregory
Comments:Submitted by A. Irving
Plots: O isotopes:  
   and collections
UWS: University of Washington, Department of Earth and Space Sciences, 70 Johnson Hall, Seattle, WA 98195, United States (institutional address; updated 15 Jan 2012)
DGregory: David Gregory, 230 First Avenue, Suite 108, St. Thomas, Ontario N5R 4P5, Canada (private address)
OkaU: Institute for Study of the Earth's Interior, Okayama University, Misasa Tottori 682-0193, Japan (institutional address)
References: Published in Meteoritical Bulletin, no. 100, MAPS 49, E1-E101 (2014)
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     This is 1 of 9776 approved meteorites from (Northwest Africa) (plus 1862 unapproved names)

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