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Northwest Africa 2191
Basic information Name: Northwest Africa 2191
     This is an OFFICIAL meteorite name.
Abbreviation: NWA 2191
Observed fall: No
Year found: 2018
Country: (Northwest Africa)
Mass:help 342 g
Classification
  history:
Recommended:  Eucrite-mmict    [explanation]

This is 1 of 224 approved meteorites classified as Eucrite-mmict.   [show all]
Search for other: Achondrites, Eucrites, and HED achondrites
Comments: Approved 7 Nov 2019
Writeuphelp
Writeup from MB 108:

Northwest Africa 2191 (NWA 2191)

(Northwest Africa)

Purchased: Jan 2018

Classification: HED achondrite (Eucrite, monomict)

History: The meteorite was exported from Morocco to Tucson where it was purchased by N. Gessler.

Physical characteristics: About 4/5 of the surface was fusion crusted; 1/4 was covered with caliche. Cut surfaces show the groundmass has a distinctive, pale-greenish grey color, except where broken by abundant (~5%) millimeter-sized patches and streaks of root-beer brown, likely oxidization zones around former scattered Fe-metals.

Petrography: The sample shows very limited, localized brecciation. It consists dominantly of pyroxene and plagioclase, along with subequal proportions of silica, olivine and ilmenite, and lesser troilite, metal (and more abundant Fe-oxide apparent products of metal weathering) and apatite. Grain sizes are diverse from place to place. Grain lengths are locally up to1 mm but more commonly a small fraction of that, and several enclaves consist of dominantly equant grains of order 5-10 µm across. The original igneous texture was dominantly subophitic, but was uneven and is now somewhat obscured due to thermal metamorphism (and possibly metasomatism), which manifests as thin exsolution lamellae mainly in pyroxene cores, complex "cloudiness" of microinclusions, and localized annealing textures.

Geochemistry: Low-Ca pyroxene clusters near Fs68Wo1.8, augite near Fs31Wo43, both unusually ferroan for a eucrite. Pyroxene FeO/MnO averages (118 analyses) 32.6. Plagioclase (31 analyses) is An59-94, average An75+/-12. Olivine (7 analyses) is uniformly Fa86-88. The aphanitic enclaves show phase compositions indistinguishable from the coarsest areas of the rock. X-ray maps document that within the larger pyroxenes strong Ca zoning survived through the thermal metamorphism. Surviving metal is extremely Ni-poor (undetectable by EDS analysis). The bulk composition, determined by INAA and fused-bead EPMA, with similar results from 2 chips totaling 700 mg, backed up by analyses of fusion crust, is uncommonly evolved for a eucrite: bulk Mg/(Mg+Fe) ~ 28 mol%, 1.4 wt% TiO2, 0.63 wt% Na2O, and Ga ~ 2.7 µg/g (further confirming evolved-eucrite affinity, by implying 1000Ga/Al = 0.047, commensurate with Na/Al = 0.084).

Classification: Eucrite, monomict breccia.

Specimens: Main mass with Gessler, type specimen, including multiple thin sections, at UCLA.

Data from:
  MB108
  Table 0
  Line 0:
Place of purchase:Tucson
Date:P Jan 2018
Mass (g):342
Pieces:1
Class:Eucrite-mmict
Shock stage:S3
Weathering grade:moderate
Fayalite (mol%):87
Ferrosilite (mol%):68 (low-Ca), 31 (high-Ca)
Wollastonite (mol%):1.8 (low-Ca), 43 (high-Ca)
Classifier:P. Warren, UCLA
Type spec mass (g):32
Type spec location:UCLA
Main mass:Nick Gessler
Finder:Anonymous
Comments:Gessler's address: 2010 Calgary Lane, Los Angeles, CA 90077; submitted by Paul Warren
Institutions
   and collections
UCLA: Institute of Geophysics and Planetary Physics, University of California, Los Angeles, CA 90095-1567, United States (institutional address; updated 17 Oct 2011)
Gessler: Nicholas Gessler, 2010 Calgary Lane, Los Angeles, CA 90077, United States (private address; updated 7 Jul 2016)
Catalogs:
References: Published in Meteoritical Bulletin, no. 108, in preparation (2019)
Find references in NASA ADS:
Find references in Google Scholar:
Geography: 
Coordinates:Unknown.

Statistics:
     This is 1 of 7005 approved meteorites from (Northwest Africa) (plus 2002 unapproved names)

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