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Northwest Africa 8186
Basic information Name: Northwest Africa 8186
     This is an OFFICIAL meteorite name.
Abbreviation: NWA 8186
Observed fall: No
Year found: 2013
Country: (Northwest Africa)
Mass:help 5.9 g
Meteoritical Bulletin:  MB 103  (2014)  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 Feb 2014
Writeup from MB 103:

Northwest Africa 8186 (NWA 8186)

(Northwest Africa)

Purchased: 2013

Classification: Ungrouped achondrite

History: Purchased from a dealer in Morocco in 2013 by Steve Witt and Mr. Smara Addi.

Physical characteristics: Single complete stone, slightly weathered, covered in black fusion crust, saw-cut reveals a fresh, fine-grained mix of green, white, and shiny metallic-luster crystals, also a black shock melt veinlet observed, friable.

Petrography: (C. Agee, UNM) Microprobe examination of a polished mount shows a highly equilibrated texture with numerous triple junction grain boundaries, significant fracturing present suggests high shock level. Olivine (up to 1 mm) is the dominant phase ~80%, plagioclase (up to 200 μm) ~10%, oxides (magnetite, hercynite-spinel, ilmenite; up to 200 μm) ~5%, augite ~3%, Cl-rich apatite ~1%, small amounts of Fe,Ni sulfide (most likely pentlandite), fusion crust (~150 μm thick) shows fine heterogeneous quench crystals of silicates and oxides.

Geochemistry: (C. Agee and H. Miley, UNM) Olivine Fa34.8±0.4, Fe/Mn=129±10, NiO=0.81±0.36 wt%, n=7; augite Fs11.8±0.4Wo48.0±0.5, Fe/Mn=179±72, n=7; plagioclase An52.3±4.6Ab45.8±4.4Or1.9±0.2, n=15; magnetite with Cr2O3=5.83±0.74, Al2O3=3.00±0.36 (wt%), n=8; hercynite-spinel Al2O3=51.06±3.70, FeO=33.31±3.98, MgO=8.20±0.58, Cr2O3=8.39±0.48 (wt%), n=5; ilmenite TiO2=30.89, Al2O3=4.08, Cr2O3=5.93, FeO=54.72, MgO=1.96 (wt%); fusion crust (proxy for bulk composition): SiO2=40.9±6.1, A2O3=2.2±0.9, FeO=24.6±3.3, MgO=28.4±5.8, CaO=2.8±0.8, Na2O=0.6±0.4 (wt%). Oxygen isotopes (Karen Ziegler, UNM) Oxygen isotope values of 3 acid-washed aliquots of bulk sample, 1.5, 1.6, 1.8 mg, gave δ17O = -4.119, -4.118, -4.378, δ18O = -0.069, -0.022, -0.176, Δ17O = -4.083, -4.106, -4.285 (linearized, all permil).

Classification: Achondrite (ungrouped). This is a unique achondrite with oxygen isotopic values identical to some CV/CK carbonaceous chondrites. Oxygen isotopic values are similar to the ungrouped achondrite NWA 7822, however this meteorite has values that are on the CCAM with significantly higher δ18O than NWA 7822. It does not appear to be paired with NWA 7822 in that it contains no Fe-Ni metal or troilite, but instead has magnetite, hercynite-spinel, ilmenite, Cl-rich apatite, and olivines and pyroxenes with higher Fe/Mn. The lack of Fe-Ni metal, the ubiquity of magnetite, and the high Ni-content of olivine indicates that this meteorite was formed at relatively high fO2 and suggests that it could have been derived from a CK carbonaceous chondrite-like precursor. Low weathering grade.

Specimens: 1.9 g including a probe mount on deposit at UNM, Steve Witt holds the main mass.

Data from:
  Table 0
  Line 0:
Place of purchase:Morocco
Date:P 2013
Mass (g):5.9
Shock stage:high
Weathering grade:low
Fayalite (mol%):34.8±0.4
Ferrosilite (mol%):11.8±0.4
Wollastonite (mol%):48.0±0.5
Classifier:C. Agee, UNM
Type spec mass (g):5.9
Type spec location:UNM
Main mass:Steve Witt
Comments:Field name SW13-9; submitted by C. Agee, UNM
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)
References: Published in Meteoritical Bulletin, no. 103, MAPS 52, 1014, May 2017, http://onlinelibrary.wiley.com/doi/10.1111/maps.12888/full
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Photos uploaded by members of the Encyclopedia of Meteorites.
    (Caution, these are of unknown reliability)
Steve Witt   

     This is 1 of 9429 approved meteorites from (Northwest Africa) (plus 1876 unapproved names)

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