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Northwest Africa 7809
Basic information Name: Northwest Africa 7809
     This is an OFFICIAL meteorite name.
Abbreviation: NWA 7809
Observed fall: No
Year found: 2013
Country: (Northwest Africa)
Mass:help 230 g
Classification
  history:
Meteoritical Bulletin:  MB 102  (2013)  Aubrite
Recommended:  EH-melt rock    [explanation]

This is 1 of 7 approved meteorites classified as EH-melt rock.   [show all]
Search for other: EH chondrites, Enstatite chondrites, Enstatite chondrites (type 4-7), Enstatite-rich meteorites, and Melted chondrites
Comments: Approved 14 Nov 2013
Revised 11 May 2019: Reclassification
Writeuphelp
Writeup from MB 102:

Northwest Africa 7809 (NWA 7809)

(Northwest Africa)

Purchased: 2013 Feb

Classification: Enstatite achondrite (Aubrite)

History: Purchased by Jason Utas in February 2013 from a Moroccan dealer at the Tucson Gem and Mineral Show.

Physical characteristics: Light colored granular stone (230 g) with orange staining.

Petrography: (A. Irving and S. Kuehner, UWS) Relatively equigranular aggregate of predominantly enstatite with accessory albite, Si-bearing kamacite, Ti-Cr-bearing troilite and daubreelite. The specimen is cross-cut by thin goethite veins.

Geochemistry: Enstatite (Fs0.3-0.5Wo0.1-0.4).

Classification: Aubrite.

Specimens: 20.1 g of material and one polished thin section are at UWB. The remaining material is held by JUtas.


Writeup from MB 108:
NWA 7809: reclassification.

NWA 4799, NWA 7214, NWA 7809, and NWA 11071 contain unfractionated modal abundances of plagioclase, troilite, and metal, which is similar to other enstatite chondrite meteorites. These NWA samples contain higher abundances of metal (7-14 vol.%) compared to aubrites. The only silicate phases in these samples are enstatite and plagioclase, whereas aubrites present olivine and diopside. Meteorites of enstatite chondrite parentage typically do not contain diopside or olivine. Other distinguishing features are metal/troilite ratios and Ti concentrations in troilite. Aubrites contain lower metal/troilite ratios and high Ti in troilite, whereas enstatite chondrite meteorites show the opposite characteristics (as these NWA meteorites do). The metal in these samples presents a higher concentration of Si compared to the aubrites (4 wt.% Si in the NWA samples versus 0.9 wt. % Si in aubrites. Graphite was also observed in these samples, which is not typically found in aubrites. The NWA meteorites show an affinity for an EH chondritic parent body origin, as seen by low Ti in troilite, high Si in metals, the presence of niningerite and graphite, and the lack of diopside and forsterite.  As metal and troilite are observed as inclusions within enstatite grains, it suggests the rocks were formed by complete melting. For the complete petrographic, mineralogical and geochemical analyses of these four meteorites, and references to data listed above, see Udry et al. (2019)
Bibliography:
  • Udry A., Wilbur Z.E., Rahib R.R., McCubbin F.M., Vander Kaaden K.E., McCoy T.J., Ziegler K., Gross J., DeFelice C., Combs L., and Turrin B.D. (2019) Reclassification of four aubrites as enstatite chondrite impact melts: Potential geochemical analogs for Mercury. Meteorit. Planet. Sci. 54, 785-810 (link)
Data from:
  MB102
  Table 0
  Line 0:
Place of purchase:Tucson
Date:P 2013 Feb
Mass (g):230
Pieces:1
Class:Aubrite
Shock stage:low
Weathering grade:moderate
Ferrosilite (mol%):0.3-0.5
Wollastonite (mol%):0.1-0.4
Classifier:A. Irving and S. Kuehner, UWS
Type spec mass (g):20.1
Type spec location:UWB
Main mass:Utas
Comments:SH13-5; submitted by A. Irving
Institutions
   and collections
UWS: University of Washington, Department of Earth and Space Sciences, 70 Johnson Hall, Seattle, WA 98195, United States (institutional address; updated 15 Jan 2012)
UWB: University of Washington, Box 353010 Seattle, WA 98195, United States (institutional address; updated 27 Jul 2012)
JUtas: Jason Utas, United States (private address; updated 8 Jun 2010)
Catalogs:
References: Published in Meteoritical Bulletin, no. 102, MAPS 50, 1662, September 2015
Published in Meteoritical Bulletin, no. 108, in preparation (2019)
Find references in NASA ADS:
Find references in Google Scholar:
Geography: 
Coordinates:Unknown.

Statistics:
     This is 1 of 6900 approved meteorites from (Northwest Africa) (plus 2035 unapproved names)

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