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Northwest Africa 16293
Basic information Name: Northwest Africa 16293
     This is an OFFICIAL meteorite name.
Abbreviation: NWA 16293
Observed fall: No
Year found: 2018
Country: (Northwest Africa)
Mass:help 153 g
Classification
  history:
Meteoritical Bulletin:  MB 112  (2024)  LL4-6
Recommended:  LL4-6    [explanation]

This is 1 of 91 approved meteorites classified as LL4-6.   [show all]
Search for other: LL chondrites, LL chondrites (type 4-7), Ordinary chondrites, and Ordinary chondrites (type 4-7)
Comments: Approved 13 Nov 2023
Writeuphelp
Writeup from MB 112:

Northwest Africa 16293 (NWA 16293)

(Northwest Africa)

Purchased: 2018

Classification: Ordinary chondrite (LL4-6)

History: A single 153 g stone was purchased online in 2018 from a Moroccan seller. Six slices totaling 26.8 g were given to Cascadia.

Physical characteristics: Physical Characteristics: Cut faces show abundant rounded and ovoid light gray clasts and a few dark-gray to black clasts set in a medium- to dark-gray matrix.

Petrography: (M. Hutson, A. Ruzicka, Cascadia): The ovoid light gray clasts seen in hand specimen are texturally different in thin section and are referred to as white or light clasts. White clasts are very light-colored, lack any evidence of chondrules, and contain plagioclase feldspar grains (up to 150 µm across) easily visible with an optical microscope. Clast 4 (>13 × 4.5 mm across, cut by section edge) is the largest white clast; twins were observed in cross-polarized light in one large plagioclase feldspar grain. Light clasts contain bright fragments and chondrules with poorly defined margins separated by slightly darker fine-grained material. Clast 5 is the largest light clast, is triangular in shape (4 mm base × 6 mm height), and fills in the space between clast 4 and another white clast. A couple of largely opaque clasts (referred to as dark clasts) are present. Clast 1 is the largest dark clast and is ovoid in shape (2 mm × 1.2 mm). The clast is composed of small (most grains much less than a maximum of 200 µm) sub-angular to sub-rounded grains of olivine and pyroxene, with plagioclase feldspar (~40 µm across).

Geochemistry (M. Hutson, A. Ruzicka, Cascadia): Eight of the larger clasts (four white, two light, one dark, and one matrix) were analyzed. Although the compositions of olivine and pyroxene grains for each clast plot within the range for LL group chondrites on a diagram of Fa vs. Fs, olivine and pyroxene compositions plot slightly outside the range for LL group chondrites on diagrams of Fa vs. Fa s.d., and Fs vs. Fs s.d. Average white clast: olivine: Fa32.0±0.5, N=34; low-Ca pyroxene: Fs26.1±0.5Wo3.1±0.8, N=22; plagioclase feldspar: Ab82.7±4.1An14.3±4.8Or2.9±1.2, N=22. Average light clasts: olivine: Fa32.0±0.8, N=21; low-Ca pyroxene: Fs23.5±3.4Wo2.1±1.1, N=22; plagioclase feldspar for 5 out of 6 grains analyzed: Ab80.0±6.1An16.9±6.1Or3.1±1.1, N=5. The sixth grain is Or-rich: Ab30.3An3.8Or65.9 and is similar to that reported by Kovach and Jones (2010) for Tuxtuac (LL5). Dark clast: olivine: Fa31.7±0.8, N=3; low-Ca pyroxene Fs25.8±1.2Wo1.8±0.9, N=3. Matrix: olivine: Fa32.0±0.8, N=12; low-Ca pyroxene: Fs24.1±1.4Wo1.4±0.8, N=20. The largest metal grains in the thin section were analyzed. All of the large grains were Ni-rich, with Ni between 41.4 and 51.8 wt% (N=52). A few small grains (~ 50 µm across) of another metallic phase were visible in BSE images as inclusions or along edges of the high-Ni metal. Analyses (excluding Co) had low totals, with Ni between 2.6 and 3.8 wt% (N=5). The Ni-beta peak was strongly asymmetric, suggesting the presence of a significant amount of Co. These grains appear to be the high-Co phase described by Rubin (1990), which states that this phase is not kamacite. Oxygen isotopic compositions (K. Ziegler, UNM) of three acid treated aliquots: 1.50 mg δ17O=3.884, 4.100, 4.048; δ18O=5.412, 5.804, 5.724; Δ17O = 1.027, 1.035, 1.046 (all ‰, slope of 0.528, sample mass 1.50 mg, 1.40 mg, 1.70 mg respectively).

Classification: Ordinary chondrite (LL4-6), based on texture (including coarseness of plagioclase feldspar) and mineral chemistry, including degree of equilibration of orthopyroxene. White clasts are LL6, light clasts are L4. Dark clast is fragmental and both olivine and pyroxene are equilibrated. This meteorite is an unusually oxidized member of the LL-group as the iron contents in olivine and pyroxene grains in most clasts are outside of the range for equilibrated LL chondrites when standard deviation is considered. Typical LL-chondrite kamacite is missing; almost all of the metal has a high Nickel content. Oxygen isotopes are at the high end of δ18O for LL chondrites, and are similar to those reported for Northwest Africa 11811 (LL5-an).

Specimens: Cascadia holds 23.7 g in seven pieces, as well as a polished thin section and material in an epoxy butt.

Bibliography:
  • Kovach H. A. and Jones R. H. (2010) Feldspar in type 4–6 ordinary chondrites: Metamorphic processing on the H and LL chondrite parent bodies. Meteoritics & Planetary Science 45, 246–264. ? (link)
  • Rubin A.E. (1990) Kamacite and olivine in ordinary chondrites - Intergroup and intragroup relationships. Geochhim. Cosmochim. Acta 54 1217-1232 (link)
Data from:
  MB112
  Table 0
  Line 0:
Place of purchase:online
Date:P 2018
Mass (g):153
Pieces:1
Class:LL4-6
Weathering grade:W1
Fayalite (mol%):32.0, 32.0, 31.7, 32.0
Ferrosilite (mol%):26.1, 23.5, 25.8, 24.1
Wollastonite (mol%):3.1, 2.1, 1.8, 1.4
Classifier:M. Hutson and A. Ruzicka, Cascadia
Type spec mass (g):26.8
Type spec location:Cascadia
Main mass:Craig Zlimen and Julie Michels, Minnesota Meteorites
Comments:Lab number CML 1655, Craig Zlimen number Zli 082; submitted by Melinda Hutson
Plots: O isotopes:  
Institutions
   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)
UNM: Institute of Meteoritics MSC03 2050 University of New Mexico Albuquerque NM 87131-1126 USA, United States; Website (institutional address; updated 12 Feb 2015)
Catalogs:
References: Published in Gattacceca J., McCubbin F. M., Grossman J. N., Schrader D. L., Cartier C., Consolmagno G., Goodrich C., Greshake A., Gross J., Joy K. H., Miao B. and Zhang B. (2024) The Meteoritical Bulletin, no. 112. Meteoritics & Planetary Science 59, 1820–1823. ?
Find references in NASA ADS:
Find references in Google Scholar:
Geography: 
Coordinates:Unknown.

Statistics:
     This is 1 of 9790 approved meteorites from (Northwest Africa) (plus 1854 unapproved names)

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