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Northwest Africa 7357
Basic information Name: Northwest Africa 7357
     This is an OFFICIAL meteorite name.
Abbreviation: NWA 7357
Observed fall: No
Year found: 2019
Country: Morocco
Mass:help 271 g
Recommended:  Eucrite-cm    [explanation]

This is 1 of 55 approved meteorites classified as Eucrite-cm.   [show all]
Search for other: Achondrites, Eucrites, and HED achondrites
Comments: Approved 5 Apr 2020
Writeup from MB 109:

Northwest Africa 7357 (NWA 7357)


Purchased: 2019

Classification: HED achondrite (Eucrite, cumulate)

Physical characteristics: The stone’s surface is half covered by fusion crust, which manifests streaming of melt. In places the surface shows significant tan-orange weathering and caliche staining. On interior broken surfaces, light mineral clasts fluoresce orange under 365 nm UV light.

Petrography: This highly shocked breccia consists dominantly of pyroxene and plagioclase (now partly maskelynite). Vaguely discernible vestiges of an original texture, and macroscopic observations, suggest grains were typically much coarser than 1 mm, but most of the material has been either granulated to much finer than 1 mm or shock-melted. A distinctive aspect of the texture is that a component of inferred likely shock-melt origin is dominantly neither glassy nor in the form of veins: Many large areas, constituting about 30% of the rock, show a crystalline but incongruously fine-grained (<20 μm) and subophitic texture, of suspected in situ, or near-in situ, impact-melt origin. This mode of origin is inferred from the sharp textural disparity with, and yet close geochemical similarity to, the surrounding coarser groundmass (which is of distinctively magnesian-cumulate composition; see below). Accessory phases include Cr-spinel, Fe-metal, troilite, and a glassy shock-melt vein. Within a few relatively ungranulated pyroxene grains, exsolved augite lamellae are seen to be typically about 4-7 μm wide. Classification as a cumulate eucrite is based on geochemistry (see below), not the severely impact-modified texture.

Geochemistry: Low-Ca pyroxene (32 analyses) clusters near Fs34.4Wo2.5. High-Ca pyroxene blebs and lamellae (4 analyses) cluster near Fs14.8Wo43.6. As a subset, pyroxenes in the fine-grained/subophitic enclaves (18 analyses) are not compositionally distinctive, apart from showing mostly intermediate Ca (Wo, 3.2-17.4 mol%), as their low-Ca and high-Ca components are not resolved by EPMA. Pyroxene FeO/MnO (wt; 36 analyses) averages 28.3. Plagioclase (8 analyses) is An92.2-93.7, average An92.6±0.5; which includes a subset of 3 analyses, averaging An93.1, from the fine-grained/subophitic domains. The fine-grained/subophitic domains are thus geochemically fully as cumulate-like as the less shocked, coarser balance of the rock. Classification as a cumulate eucrite is based on geochemistry (consistently magnesian mafic silicates, Na-poor plagiolcase, far more Cr-spinel than ilmenite), not texture. Analyses (6) of a long glassy shock-melt vein average 19.3±1.3 wt% Al2O3 with FeO/MgO (wt) = 1.05.

Classification: Eucrite, cumulate, brecciated.

Specimens: 24 g at UCLA; main mass (5 kg) with Gessler.

Data from:
  Table 0
  Line 0:
Place of purchase:Mailed from Morocco
Date:P 2019
Mass (g):271
Shock stage:High
Weathering grade:moderate
Ferrosilite (mol%):34.3±1.1 (low-Ca)
Wollastonite (mol%):2.9±0.6 (low-Ca)
Classifier:P Warren, UCLA
Type spec mass (g):24
Type spec location:UCLA
Main mass:Nick Gessler
Comments:Gessler's address: 2010 Calgary Lane, Los Angeles, CA 90077; submitted by Paul Warren
   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)
References: Published in Meteoritical Bulletin, no. 109, in preparation (2020)
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     This is 1 of 1967 approved meteorites from Morocco (plus 37 unapproved names) (plus 1 impact crater)

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