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Northwest Africa 13355
Basic information Name: Northwest Africa 13355
     This is an OFFICIAL meteorite name.
Abbreviation: NWA 13355
Observed fall: No
Year found: 2020
Country: (Northwest Africa)
Mass:help 672 g
Classification
  history:
Recommended:  Eucrite-an    [explanation]

This is 1 of 15 approved meteorites classified as Eucrite-an.   [show all]
Search for other: Achondrites, Eucrites, and HED achondrites
Comments: Approved 19 Jul 2020
Writeuphelp
Writeup from MB 109:

Northwest Africa 13355 (NWA 13355)

(Northwest Africa)

Purchased: 2020 May

Classification: HED achondrite (Eucrite, anomalous)

History: Purchased by Rachid Chaoui in May 2020 from a Mauritanian dealer.

Physical characteristics: A very dark ellipsoidal specimen (672 g) partly coated by a shiny patina and with one broken side (slightly weathered). The fresh interior is dark gray with some larger dark crystals barely visible.

Petrography: (A. Irving, UWS and P. Carpenter, WUSL) This specimen has an unbrecciated igneous texure, but is unique among eucrites in containing relatively large (up to 4 mm) subhedral phenocrysts of exsolved pigeonite with abundant thin exsolution lamellae of chromite. The prismatic phenocrysts are set in a groundmass of parallel-intergrown pigeonite and calcic plagioclase with accessory silica polymorph, Ti-chromite, ilmenite, troilite and baddeleyite.

Geochemistry: Low-Ca pyroxene host (Fs49.6-53.2Wo1.8-3.0, FeO/MnO = 31-32, N = 4), augite exsolution lamellae (Fs23.1-25.0Wo39.6-42.7, FeO/MnO = 29-31, N = 2), plagioclase (An79.2-85.5Or6.5-0.6, N = 4). Oxygen isotopes (K. Ziegler, UNM): analyses of acid-washed bulk subsamples by laser fluorination gave, respectively, δ17O 1.665, 1.895, 1.871; δ18O 3.693, 4.157, 4.105; Δ17O -0.285, -0.300, -0.296 per mil. These results plot beyond the main field for eucrites to more negative Δ17O values.

Classification: Eucrite (unbrecciated, pyroxene-phyric, anomalous). The porphyritic igneous texture, prominent chromite exsolution in pyroxenes and atypical oxygen isotopic composition are anomalous features. Chromite exsolution from pyroxene has been documented in ungrouped achondrite GRA 06129 and some Luna 24 specimens, but not previously in eucrites.

Specimens: 23 g including one polished thin section at UWB; remainder with Mr. R. Chaoui.

Data from:
  MB109
  Table 0
  Line 0:
Place of purchase:Mauritania
Date:P 2020 May
Mass (g):672
Pieces:1
Class:Eucrite-an
Shock stage:low
Weathering grade:low
Ferrosilite (mol%):49.6-53.2; 23.1-25.0
Wollastonite (mol%):1.8-3.0; 39.6-42.7
Classifier:A. Irving, UWS, and P. Carpenter, WUSL
Type spec mass (g):23.0
Type spec location:UWB
Main mass:R. Chaoui
Comments:Work name RC124.1; submitted by A. Irving
Plots: O isotopes:  
Institutions
   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)
UWS: University of Washington, Department of Earth and Space Sciences, 70 Johnson Hall, Seattle, WA 98195, United States (institutional address; updated 15 Jan 2012)
WUSL: Washington Univ., One Brookings Drive, St. Louis, MO 63130, United States (institutional address; updated 17 Oct 2011)
UWB: University of Washington, Box 353010 Seattle, WA 98195, United States (institutional address; updated 27 Jul 2012)
Catalogs:
References: Published in Meteoritical Bulletin, no. 109, in preparation (2020)
Find references in NASA ADS:
Find references in Google Scholar:
Geography: 
Coordinates:Unknown.

Statistics:
     This is 1 of 9305 approved meteorites from (Northwest Africa) (plus 1873 unapproved names)

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