Official Meteoritical Bulletin entry for Northwest Africa 4880:
Northwest Africa 4880 Algeria Find: 2005 (additional paired stones discovered in 2007) Achondrite (Martian, basaltic shergottite)
(Original NWA 2975 classification that NWA 4880/4930 and other pairings conform to): 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.
Wittke J.H., Bunch T.E., Herd C.D.K., Lapan T.J., Rumble D. Irving A.J. and Pitt D.
(2010) Petrology and composition of “enriched” mafic Shergottite Northwest Africa 5718:
Contrasts with Northwest Africa 2975/2986 (abs#5313). Meteorit. & Planet. Sci. 45, A217. http://www.lpi.usra.edu/meetings/metsoc2010/pdf/5313.pdf
Rumble D. and Irving A.J.
(2009) Dispersion of oxygen isotopic compositions among 42 Martian meteorites determined by laser fluorination:
Evidence for assimilation of (ancient) altered crust (abs#2293). Lunar Planet. Sci. XL,
Lunar Planetary Institute @ The Woodlands. http://www.lpi.usra.edu/meetings/lpsc2009/pdf/2293.pdf
Connolly H.C. and 11 authors
(2006) The Meteoritical Bulletin, No. 90. Meteorit. & Planet. Sci.41, 1383-1418.
Wittke J.H., Bunch T.E., Irving A.J., Farmer M. and Strope J.
(2006) Northwest Africa 2975: An evolved basaltic Shergottite with vesicular
glass pockets and trapped melt inclusions (abs#1368). Lunar Planet. Sci.XXXVII,
Lunar Planetary Institute, Houston. http://www.lpi.usra.edu/meetings/lpsc2006/pdf/1368.pdf
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