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Northwest Africa 12689
Basic information Name: Northwest Africa 12689
     This is an OFFICIAL meteorite name.
Abbreviation: NWA 12689
Observed fall: No
Year found: 2014
Country: Morocco
Mass:help 629 g
Classification
  history:
Recommended:  Eucrite-br    [explanation]

This is 1 of 161 approved meteorites classified as Eucrite-br.   [show all]
Search for other: Achondrites, Eucrites, and HED achondrites
Comments: Approved 10 Jul 2019
Writeuphelp
Writeup from MB 108:

Northwest Africa 12689 (NWA 12689)

Morocco

Purchased: 2014

Classification: HED achondrite (Eucrite, brecciated)

History: A single stone of 629 g was purchased from a Moroccan dealer by Dr. R. McKenzie in 2014.

Physical characteristics: Light-brown lithic clasts 0.5 to 1.5 cm across protrude through partly preserved, dark-brown fusion crust. Cut surface shows rounded lithic clasts, some of which contain feldspar laths up to ~1 mm long, surrounded by fine grained, dark-brown to black matrix.

Petrography: (L. Vonopartis and L. Ashwal, Wits) A monomict eucrite breccia with angular to rounded lithic clasts up to 15 mm across, in a glassy matrix that contains mineral fragments and broken lithic clasts 0.1 to 5 mm across. Most of the lithic clasts are composed of subequal proportions of coarse-grained, subhedral plagioclase laths up to 1.2 mm long, surrounded by irregular sub-ophitic grains of low-Ca pyroxene, many of which contain augite exsolution lamellae of variable thickness. The overall texture of these lithic clasts resembles terrestrial dolerites or coarse-grained basalts, but differs from the coarse, equigranular textures typical of unbrecciated cumulate eucrites. A small proportion of lithic clasts consist of fine-grained (0.01 to 0.05 mm) granoblastic aggregates of plagioclase and pyroxene, with angular mineral fragments up to 0.5 mm across. The matrix consists of dark brown, partly devitrified glass with some evidence for flow textures, which is charged with highly comminuted lithic and mineral fragments 0.01 to 0.5 mm across, very likely representing fragmental material derived from the larger lithic clasts. Both feldspars and pyroxenes in all components of the specimen show variable shock features, including kinked and offset twins, undulatory extinction and mosaicism; some plagioclases have been completely maskelynitized. Accessory minerals include chromite, ilmenite and a silica phase.

Geochemistry: Mineral compositions and geochemistry: (L. Vonopartis and L. Ashwal, Wits; D. Van Niekerk, Rhodes University; R. Greenwood, OU) Low-Ca pyroxene is homogeneous (Fs59.6±1.4Wo3.4±1.4) and contains augite exsolution lamellae (Fs25.5±0.7Wo44.1±1.6). Plagioclase is somewhat more variable (Ab10.4±1.6An88.9±1.7Or0.6±0.2), but individual grains show no compositional zoning. Accessory chromite has Mg/(Mg+Fe) = 3.75 and Cr/(Cr+Al) = 80.29; ilmenite has MgO = 0.75±0.05 and MnO = 1.52±0.05. Dark brown glass in the matrix is basaltic, with SiO2 = 49.1±0.6, Al2O3 = 19.4±2.1 and Mg/(Mg+Fe) = 34.4±2.2. Oxygen isotope analyses on 150 mg of powdered sample yielded: δ17O = 1.855±0.45 ‰, δ18O = 3.997±0.10 ‰, Δ17O = -0.223±0.007 ‰.

Classification: (L. Vonopartis and L. Ashwal, Wits) Achondrite (eucrite). High degree of shock (S5), and low degree of weathering.

Specimens: Main mass 490 g held in private collection of Dr. R. McKenzie. Type specimen 86 g, and 3 chips (8, 10, 18 g) remaining after thin section preparation Wits. A 150 mg subsample from an 18 g chip was powdered and consumed for oxygen isotopic analyses at OU.

Data from:
  MB108
  Table 0
  Line 0:
Origin or pseudonym:Desert
Place of purchase:Morocco
Date:P 2014
Mass (g):629
Pieces:1
Class:Eucrite-br
Shock stage:S5
Weathering grade:minor
Ferrosilite (mol%):59.6±1.4 (N=16); 25.5±0.7 (N=13)
Wollastonite (mol%):3.4±1.1 (N=16); 44.1±0.6 (N=13)
Magnetic suscept.:2.67
Classifier:L. Vonopartis and L. Ashwal, Wits
Type spec mass (g):86
Type spec location:Wits
Main mass:Dr. R. McKenzie, WRP, Pty. Ltd, Pretoria, 0001 South Africa
Finder:Unknown
Comments:Submitted by L. Vonopartis and L. D. Ashwal
Plots: O isotopes:  
Institutions
   and collections
OU: Planetary and Space Sciences Department of Physical Sciences The Open University Walton Hall Milton Keynes MK7 6AA United Kingdom, United Kingdom (institutional address; updated 8 Dec 2011)
Wits: Curator of Fossil and Rock Collections c/o Evolutionary Studies Institute University of the Witwatersrand Private Bag 3 WITS 2050 Johannesburg South Africa, South Africa (institutional address; updated 3 May 2019)
Catalogs:
References: Published in Meteoritical Bulletin, no. 108, in preparation (2019)
Find references in NASA ADS:
Find references in Google Scholar:
Geography:

Morocco
Coordinates:Unknown.

Statistics:
     This is 1 of 1374 approved meteorites from Morocco (plus 16 unapproved names) (plus 1 impact crater)

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