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Northwest Africa 16561
Basic information Name: Northwest Africa 16561
     This is an OFFICIAL meteorite name.
Abbreviation: NWA 16561
Observed fall: No
Year found: 2023
Country: (Northwest Africa)
Mass:help 139 g
Recommended:  LL5    [explanation]

This is 1 of 3312 approved meteorites (plus 1 unapproved name) classified as LL5.   [show all]
Search for other: LL chondrites, LL chondrites (type 4-7), Ordinary chondrites, and Ordinary chondrites (type 4-7)
Comments: Approved 21 Mar 2024
Writeup from MB 113:

Northwest Africa 16561 (NWA 16561)

(Northwest Africa)

Purchased: Jan 2023

Classification: Ordinary chondrite (LL5)

History: Mr. Jasper Spencer purchased a single 139 g stone from a Mauritanian dealer in January 2023 via Facebook Messenger. The dealer said that the stone was found in Mauritania by nomads during 2022. A 23.2 g end piece was given to Cascadia for classification in October 2023.

Physical characteristics: Physical Characteristics: The exterior of the end cut received by Cascadia is medium brown in color and appears to be a weathered broken surface. The cut face is light gray with dark orange-brown patches surrounding sulfide grains. Chondrules can be discerned in the light gray regions, but are not crisply defined.

Petrography: (M. Hutson, J. Laster, and A. Ruzicka, Cascadia): Chondrules and chondrule fragments set in a granular matrix can be seen in thin section. A large (4 mm apparent diameter) spherical clast composed of coarse orthopyroxene grains and an adjacent large (~2 × 4 mm exposed area) troilite grain occur on a boundary between yellow-stained and unstained halves of the thin section. Networks of plagioclase feldspar entraining small grains (mainly of silicate minerals, chromite, and troilite), occur throughout the section, forming rims around chondrules and chondrule fragments, as well as veins cutting across chondrules. Chromite-plagioclase assemblages are visible, including as mesostasis objects in a barred olivine-pyroxene chondrule. With one exception, all of the plagioclase feldspar grains are <50 µm across. The exception is a single clast of coarse (>100 µm across) interlocking grains of twinned plagioclase feldspar grains enclosing skeletal crystals of olivine.

Geochemistry: Olivine, low-Ca pyroxene, and plagioclase feldspar are equilibrated across the section: Olivine Fa28.9±0.4, N=44; Low-Ca pyroxene Fs24.0±0.5Wo1.6±0.3, N=46; plagioclase feldspar Ab80.9±0.8Or5.6±0.6An13.5±0.3, N=10.

Classification: Ordinary chondrite (LL5) based on texture and mineral chemistry. Chondrules and chondrule fragments are readily discerned, and plagioclase feldspar throughout the section, with the exception of grains in one clast are <50 μm across. The one exception is interpreted as an annealed melt pocket.

Specimens: Cascadia holds 17.7 g in one piece, as well as a polished thin section and material in an epoxy butt; Mr. Jasper Spencer holds the main mass.

Data from:
  Table 0
  Line 0:
Place of purchase:FB Messenger
Date:P Jan 2023
Mass (g):139
Shock stage:S4
Weathering grade:W2
Fayalite (mol%):28.9±0.4 (N=44)
Ferrosilite (mol%):24.0±0.5 (N=46)
Wollastonite (mol%):1.6±0.3 (N=46)
Classifier:M. Hutson, J. Laster, and A. Ruzicka, Cascadia
Type spec mass (g):23.2
Type spec location:Cascadia
Main mass:Mr. Jasper Spencer
Comments:Lab number CML 1725; submitted by Melinda Hutson
   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)
References: Published in Meteoritical Bulletin, no. 113, in preparation (2024)
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     This is 1 of 9829 approved meteorites from (Northwest Africa) (plus 1851 unapproved names)

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