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Northwest Africa 7531
Basic information Name: Northwest Africa 7531
     This is an OFFICIAL meteorite name.
Abbreviation: NWA 7531
Observed fall: No
Year found: 2009
Country: Morocco
Mass:help 868 g
Meteoritical Bulletin:  MB 101  (2012)  CR7
Recommended:  CR7    [explanation]

This is 1 of 2 approved meteorites classified as CR7.   [show all]
Search for other: Carbonaceous chondrites, Carbonaceous chondrites (equilibrated) , CR chondrites, and CR chondrites (equilibrated)
Comments: Approved 7 Dec 2012
Writeup from MB 101:

Northwest Africa 7531 (NWA 7531)


Found: 2009

Classification: Carbonaceous chondrite (CR7 polymict breccia)

History: An anonymous buyer purchased an 868 g stone in Erfoud, Morocco in 2009.

Physical characteristics: The fresh stone has a smooth, dark ablation crust with a coarse network of shrinkage cracks.

Petrography: The interior consists of angular clasts of two lithologies. The dominant lithology comprises ~66 vol%, and is green, consisting of crushed, recrystallized coarse-grained olivine, orthopyroxene poikiloblasts (olivine chadacrysts), plagioclase, minor chromite, taenite, FeS, and Cl-apatite. Modal analyses (vol %): Orthopyroxene, 42; olivine, 37; plagioclase, 14; other, 7. The second lithology is gray, recrystallized, lacking chondrules, with coarse-grained orthopyroxene poikiloblasts (olivine chadacrysts), smaller grained olivine, minor augite, recrystallized troilite with tiny silicate entrainments, metal, merrillite, and chromite. Boundaries between clasts are occupied with a 0.5 to 1.0 mm thick layer of finely granulated, recrystallized "rock flour".

Geochemistry: The green lithology has olivine, Fa30.8, FeO/MnO = 90; orthopyroxene, Fs27.4Wo4.2, FeO/MnO = 44; plagioclase An14.7Or 5.4; chromite cr# = 90, taenite Ni = 42 wt %. The LL lithology contains olivine Fa28.6, FeO/MnO = 58; orthopyroxene, Fs24.2Wo2.0. Oxygen isotopes (D. Rumble, CIW): Replicate analyses of acid-washed material by laser fluorination gave, respectively for the greenish lithology Δ17O = -0.988 and -0.978; δ17O = 2.899 and 2.729; δ18O = 7.391 and 7.048. LL lithology Δ17O = 1.193 and 1.194; δ17O = 3.903 and 3.851; δ18O = 5.152 and 5.052 (all per mil). Compositional, petrographic and oxygen isotopic data for the green lithology are consistent with CR7, and LL7 for the gray lithology.

Classification: CR7 polymict breccia with an LL7 clast.

Specimens: A total of 22 g is at UWB; main mass holder is anonymous.

Data from:
  Table 0
  Line 0:
Place of purchase:Erfoud
Mass (g):868
Shock stage:low
Weathering grade:W0/1
Fayalite (mol%):30.8
Ferrosilite (mol%):27.4
Wollastonite (mol%):4.2
Classifier:T. Bunch and J. Wittke, NAU; A. Irving, UWS
Type spec mass (g):22
Type spec location:UWB
Main mass:anonymous
Comments:Polymict breccia; submitted by Bunch
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)
UWB: University of Washington, Burke Museum of Natural History and Culture, Box 353010 Seattle, WA 98195, United States (institutional address; updated 9 Oct 2023)
CIW: Carnegie Insitution Washington, Geophysical Laboratory, 5251 Broad Branch Rd., NW, Washington DC 20015, United States (institutional address)
NAU: Geology, Bldg 12 Knoles Dr Northern Arizona University, Flagstaff, AZ 86011, United States (institutional address; updated 12 Apr 2012)
References: Published in Meteoritical Bulletin, no. 101, MAPS 50, 1661, September 2015
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     This is 1 of 2118 approved meteorites from Morocco (plus 32 unapproved names) (plus 1 impact crater)

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