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Northwest Africa 11558
Basic information Name: Northwest Africa 11558
     This is an OFFICIAL meteorite name.
Abbreviation: NWA 11558
Observed fall: No
Year found: 2017
Country: (Northwest Africa)
Mass:help 3.92 g
Meteoritical Bulletin:  MB 107  (2018)  Achondrite-ung
Recommended:  Achondrite-ung    [explanation]

This is 1 of 140 approved meteorites classified as Achondrite-ung.   [show all]
Search for other: Achondrites, Ungrouped achondrites
Comments: Approved 12 Jan 2018
Writeup from MB 107:

Northwest Africa 11558 (NWA 11558)

(Northwest Africa)

Purchased: 2017 Sep

Classification: Ungrouped achondrite

History: Two identical small samples of an unusual achondrite were sent by two separate Moroccan dealers to Dr. Anthony Irving in January 2017. Later in September 2017 the remainder of one of these specimens was purchased from one of the original dealers by Ben Hoefnagels.

Physical characteristics: The friable specimens (total weight 3.92 g) are both composed of abundant white and green grains.

Petrography: (A. Irving and S. Kuehner, UWS; I. Barker and D. Moser, UWO) The specimens have a porphyritic plutonic igneous texture. The mineralogy is dominated by larger grains (1.6-2.1 mm) of anorthite, strongly zoned clinopyroxene and tridymite (identified by electron backscatter diffraction analysis). More sodic (bytownitic) plagioclase and more ferroan clinopyroxenes occur in the groundmass together with accessory orthopyroxene, ilmenite, ulvöspinel, troilite, cristobalite, minor quartz, rare low-Ni kamacite and rare baddeleyite. Some silica occurs as graphic intergrowths with clinopyroxene in the groundmass, or as very small inclusions accompanied by clinopyroxene within plagioclase.

Geochemistry: Diopside cores (Fs5.1-5.3Wo38.8-39.0, FeO/MnO = 6, N = 2), subcalcic augite (Fs37.0Wo30.9, FeO/MnO = 8), subcalcic ferroaugite (Fs67.3Wo25.8, FeO/MnO = 10), ferropigeonite(Fs69.7-78.7Wo22.3-15.4, FeO/MnO = 7-10, N = 2), plagioclase (An69.2-91.9Or1.2-0.2, N = 3). Oxygen isotopes (K. Ziegler, UNM): analyses of acid-washed subsamples by laser fluorination gave, respectively, δ17O 2.716, 3.020, 3.525; δ18O 6.990, 7.573, 8.530; Δ17O -0.975, -0.979, -0.979 per mil.

Classification: Ungrouped achondrite. This material is paired with NWA 11119 on the basis of closely similar mineralogy and identical oxygen isotopic composition. According to the IUGS nomenclature for igneous rocks (Le Maitre et al., 1989), this specimen would be a porphyritic quartz gabbro. However, given that the dominant silica polymorph is tridymite, a more appropriate designation would be tridymite gabbro.

Specimens: 2.56 g including one polished epoxy mount at UWB; 1.36 g with Mr. B. Hoefnagels.

Data from:
  Table 0
  Line 0:
Place of purchase:Morocco
Date:P 2017 Sep
Mass (g):3.92
Shock stage:low
Weathering grade:low
Ferrosilite (mol%):5.1-78.7
Wollastonite (mol%):38.8-15.4
Classifier:A. Irving and S. Kuehner, UWS
Type spec mass (g):2.56
Type spec location:UWB
Main mass:B. Hoefnagels
Comments:Work name BH127; submitted by A. Irving
Plots: O isotopes:  
   and collections
UNM: Institute of Meteoritics MSC03 2050 University of New Mexico Albuquerque NM 87131-1126 USA, United States; Website (institutional address; updated 12 Feb 2015)
UWO: University of Western Ontario, Department of Earth Sciences, BGS 1026, 1151 Richmond St. N, London, Ontario, Canada N6A 5B7, Canada (institutional address; updated 18 Jul 2015)
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)
References: Published in Meteoritical Bulletin, no. 107, MAPS 55, 460-462
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     This is 1 of 9429 approved meteorites from (Northwest Africa) (plus 1876 unapproved names)

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