|Northwest Africa 2975|
|Basic information||Name: Northwest Africa 2975|
This is an OFFICIAL meteorite name.
Abbreviation: NWA 2975
Observed fall: No
Year found: 2005
Mass: 70.1 g
This is 1 of 146 approved meteorites (plus 1 unapproved name) classified as Martian (shergottite). [show all]
Search for other: Martian meteorites
Approved 16 Jan 2006|
Revised 3 Feb 2006: Revised writeup
Writeup from MB 90:
Northwest Africa 2975
Achondrite (Martian, basaltic shergottite)
History: A minimally weathered fully encrusted whole stone of 70.1 g was purchased in Erfoud, Morocco, by M. Farmer in November 2005.
Petrography: (T. Bunch and J. Wittke, NAU; A. Irving, UWS) A medium-grained (<3.1 mm greatest dimension) basaltic shergottite that consists of ~57.3 vol% augite and pigeonite pyroxenes, and 38.3 vol% plagioclase (present as shock-formed maskelynite and glasses) with minor opaques (2.7 vol%) and phosphates (1.7 vol%) arranged in a weakly foliated subophitic to granular texture. Accessory phases include ulvöspinel, ilmenite, chlorapatite, merrillite, pyrrhotite, Si-Al-Na-K-rich glasses, and baddeleyite. Vesicular black glass veins (<3 mm in width) and pockets (up to 6 mm) are prominent.
Geochemistry: Pigeonite (Fs35.2–57.6Wo12.6–16.5; FeO/MnO = 28–38) and augite (Fs27.2–41.5Wo30.8–35.2) show mottled compositional zoning. Fe-rich margins of pigeonite contain very thin (0.2–0.5 µm) orthopyroxene exsolution lamellae. Maskelynite is compositionally homogeneous An55Or1.8 in contrast to mesostasis maskelynite (An48–60Or9.2) and glasses. Melt inclusions (15–60 µm, longest dimension) in ulvöspinel have rims of Fe-rich pigeonite (Fs73.5Wo5.8), merrillite, and pyrrhotite; cores are Si-Al-K-Na-rich glass. Bulk composition: Calculated average bulk composition based on analyzed phases and their modes of three melt inclusions is: SiO2 = 70.2, Al2O3 = 8.5, TiO2 = 0.8, FeO = 2.1, MnO = 0.2, MgO = 2.35, CaO = 3.5, Na2O = 0.95, K2O = 2. 1, and P2O5 = 2.8 (all wt%) with trace amounts of NiO, CoO, and S. One melt inclusion contains only fayalite (Fa84) mantled around a core of glass (K2O = 6.4, SiO2 = 78; both wt%).
Classification: Achondrite (Martian basaltic shergottite); moderate to high shock, minimal weathering.
Specimens: A 20.2 g type specimen and one thin section are on deposit at NAU. An anonymous owner holds the main mass.
NAU: Geology, Bldg 12
Northern Arizona University, Flagstaff, AZ 86011, United States; Website (institutional address; updated 12 Apr 2012)
UWS: University of Washington, Department of Earth and Space Sciences, 70 Johnson Hall, Seattle, WA 98195, United States (institutional address; updated 15 Jan 2012)
Farmer: Michael Farmer, P.O. Box 86059, Tucson, AZ 85754-6059, United States; Website (private address)
|References:||Published in Meteoritical Bulletin, no. 90, MAPS 41, 1383-1418 (2006)|
This is 1 of 726 approved meteorites from Algeria (plus 27 unapproved names) (plus 4 impact craters)
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