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Northwest Africa 4858
Basic information Name: Northwest Africa 4858
     This is an OFFICIAL meteorite name.
Abbreviation: NWA 4858
Observed fall: No
Year found: 2004
Country: (Northwest Africa)
Mass:help 329 g
Meteoritical Bulletin:  MB 94  (2008)  Howardite
Recommended:  Howardite    [explanation]

This is 1 of 453 approved meteorites classified as Howardite.   [show all]
Search for other: Achondrites, HED achondrites, and Howardites
Comments: Approved 15 May 2008
Writeup from MB 94:

Northwest Africa 4858

Morocco or Algeria

Find: 2004

Achondrite (howardite)

History: Purchased in July 2004 in Erfoud, Morocco, by Edwin Thompson.

Physical characteristics: A single stone weighing 329 g with a partial brown/black fusion coating.

Petrography: (A. Ruzicka and T. J. Schepker, Cascadia) In hand specimen, sample is light gray with numerous bright green crystals. It is clearly a polymict breccia with angular to subrounded clasts. These include coarse-grained diogenitic orthopyroxene clasts, which make up greater than 10% of the total material. Additionally, there are coarse-grained plagioclase mineral clasts, eucritic rock clasts that contain inverted pigeonite and plagioclase ± a silica mineral, pigeonite mineral clasts, fine-grained clasts that are interpreted to be crystallized impact melts, and some fine-grained pseudotachylite veins. Relatively rare oxide minerals are also present.

Mineral compositions and geochemistry: Most pyroxene and plagioclase grains show modest chemical zoning, but compositions between clasts differ significantly. Pyroxene types include diogentitic orthopyroxene (Wo0.7–5 En58–77 Fs21–39, n = 22), non-inverted pigeonite (Wo5–15 En37–56 Fs36–55, n = 9), inverted pigeonite, which contains lamellae of orthopyroxene (Wo3–5 En34–49 Fs46–62, n = 9), and augite (Wo41–43 En31–36 Fs21–29, n = 2). Plagioclase is fairly calcic (Ab3–15, An84–97, Or0–1, n = 33).

Classification: Achondrite (howardite). Degree of shock varies from clast to clast and evidence of shock melting in a few clasts. Weathering is minimal.

Type specimens: A total of 42 g and one thin section are on deposit at Cascadia. Thompson holds the main mass.

Data from:
  Table 2
  Line 74:
Mass (g):329
Ferrosilite (mol%):21-39, 36-35
Wollastonite (mol%):0.7-5, 5-15
Classifier:A. Ruzicka and T. J. Schepker, Cascadia
Type spec mass (g):42
Type spec location:Thompson
Main mass:Thompson
   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)
Thompson: Edwin Thompson, 5150 Dawn St., Lake Oswego, OR 97035, United States (private address)
References: Published in Meteoritical Bulletin, no. 94, MAPS 43, 1551-1588 (2008)
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     This is 1 of 9829 approved meteorites from (Northwest Africa) (plus 1851 unapproved names)

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