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Northwest Africa 11857
Basic information Name: Northwest Africa 11857
     This is an OFFICIAL meteorite name.
Abbreviation: NWA 11857
Observed fall: No
Year found: 2018
Country: (Northwest Africa)
Mass:help 580 g
Meteoritical Bulletin:  MB 107  (2018)  Diogenite
Recommended:  Diogenite    [explanation]

This is 1 of 481 approved meteorites classified as Diogenite.   [show all]
Search for other: Achondrites, Diogenites, and HED achondrites
Comments: Approved 8 Jul 2018
Writeup from MB 107:

Northwest Africa 11857 (NWA 11857)

Northwest Africa

Purchased: 2018

Classification: HED achondrite (Diogenite)

History: One stone weighing 580 g was found in Morocco prior to 2018. Steve Arnold purchased the sample from a meteorite dealer while at the 2018 Tucson Gem and Mineral Show.

Physical characteristics: The uncrusted sample has a weathered orangish-yellow exterior and yellowish-orange interior that is brecciated and friable. The cut face shows angular-subrounded clasts up to 5 mm in the long dimension.

Petrography: Description and classification (A. Love, App): Sample is a breccia composed of diogenitic lithic fragments (with average grainsize of 681 μm) and coarser grained (~1287 μm) cataclastic clasts mixed within a comminuted host of similar materials. Lithic clasts are composed of interlocking, orthopyroxenes, which share 120º grain boundaries. Orthopyroxenes contain CPX inclusions and exsolution lamellae (up to 0.5mm) within crystals. Additional minerals are Si polymorphs, chromite, FeS and rare Ni-free iron metal.

Geochemistry: (A. Love, App) Low-Ca pyroxene host Fs26.2±0.6 Wo2.8±0.7 (Fs26.2-28.0Wo1.8-3.6, FeO/MnO=26.3-27.6 , N=12); high-Ca pyroxene inclusions and exsolution lamellae Fs10.6±0.5Wo44.0±1.2 (Fs9.9-11.6Wo41.9-45.7, FeO/MnO=20.1-21.2 N=6)

Classification: HED (monomict diogenite breccia). Textures, FeO/MnO and Fs compositions of pyroxenes indicate this sample is a diogenite.

Specimens: Steve Arnold holds the main mass. One 20 g endcut, several fragments and a polished thin section are on deposit at App.

Data from:
  Table 0
  Line 0:
Place of purchase:Tucson Gem and Mineral Show
Date:P 2018
Mass (g):580
Shock stage:low
Weathering grade:low
Ferrosilite (mol%):26.2±0.6; 10.6±0.5
Wollastonite (mol%):2.8±0.7; 44.0±1.2
Classifier:A. Love, App
Type spec mass (g):20
Type spec location:App
Main mass:Steve Arnold
Comments:Submitted by Anthony Love
   and collections
App: Department of Geology, 572 Rivers St., Appalachian State University, Boone, NC 28608, United States (institutional address; updated 7 Mar 2013)
References: Published in Meteoritical Bulletin, no. 107, MAPS 55, 460-462
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     This is 1 of 8025 approved meteorites from (Northwest Africa) (plus 1951 unapproved names)

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