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Northwest Africa 11991
Basic information Name: Northwest Africa 11991
     This is an OFFICIAL meteorite name.
Abbreviation: NWA 11991
Observed fall: No
Year found: 2018
Country: (Northwest Africa)
Mass:help 1020 g
Meteoritical Bulletin:  MB 107  (2018)  LL3
Recommended:  LL3    [explanation]

This is 1 of 496 approved meteorites classified as LL3.   [show all]
Search for other: LL chondrites, LL chondrites (type 3), Ordinary chondrites, and Ordinary chondrites (type 3)
Comments: Approved 9 Oct 2018
Writeup from MB 107:

Northwest Africa 11991 (NWA 11991)

(Northwest Africa)

Purchased: 2018 Jan

Classification: Ordinary chondrite (LL3)

History: Found in northwest Africa.

Physical characteristics: In cut slices, interior is light gray to light brown with slight weathering staining, has well defined chondrules and metal contents typical of LL chondrites.

Petrography: (A. Ruzicka, S. Goudy, Cascadia) Thin section shows well-defined chondrules, many with glassy mesostases, and good examples of cluster chondrite texture with little intervening matrix. Multiple bleached chondrules. Analysis in reflected light shows thin section contains roughly 2.3% metal with ~10% metal weathered, and roughly 4.2% troilite; largest slice contains 2.8±0.3% metal and 5.4±0.6% troilite (area% values). Based on olivine, shock stage is S5. Matrix is composed chiefly of <10 μm grains of ferroan olivine and albitic feldspar, reminiscent of that found in Lut 005 and Lut 006.

Geochemistry: (M. Hutson, Cascadia) Olivine (Fa21.6±9.9, N = 156; Cr2O3 0.07±0.05 wt%, N = 126).

Classification: LL3, estimated subtype 3.5. LL indicated by low metal content and minor weathering. Type 3 indicated by texture, presence of chondrule glass, and variable olivine composition. Subtype estimated as 3.5 based on olivine Fa variability (subtype 3.4-3.6) and chrome content in olivine.

Specimens: A total of 48.4 g in two slices, a polished thin section, and potted butt are available at Cascadia. Mr. James Tobin holds the main mass.

Data from:
  Table 0
  Line 0:
Place of purchase:Tucson
Date:P 2018 Jan
Mass (g):1020
Shock stage:S5
Weathering grade:W1
Fayalite (mol%):21.6
Classifier:M. Hutson, S. Goudy, A. Ruzicka, Cascadia
Type spec mass (g):48.4
Type spec location:Cascadia
Main mass:Tobin
Comments:Specimen number CML0091.; submitted by Alex Ruzicka
   and collections
Cascadia: Cascadia Meteorite Laboratory, Portland State University, Department of Geology, Room 17 Cramer Hall, 1721 SW Broadway, Portland, OR 97201, United States; Website (institutional address; updated 28 Oct 2011)
Tobin: J. Tobin, The Meteorite Exchange, PMB #455, P.O. Box 7000, Redondo Beach, CA 90277, United States (private address)
References: Published in Meteoritical Bulletin, no. 107, MAPS 55, 460-462
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     This is 1 of 9806 approved meteorites from (Northwest Africa) (plus 1855 unapproved names)

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