New Martian Shergottite Meteorite
Official Classification by Dr. Ted Bunch of Northern Arizona University and Dr. Tony Irving of the University of Washington, below:
Northwest Africa 2975
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 (Fs35.257.6Wo12.616.5; FeO/MnO = 2838) and augite (Fs27.241.5Wo30.835.2) show mottled compositional zoning. Fe-rich margins of pigeonite contain very thin (0.20.5 µm) orthopyroxene exsolution lamellae. Maskelynite is compositionally homogeneous An55Or1.8 in contrast to mesostasis maskelynite (An4860Or9.2) and glasses. Melt inclusions (1560 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.
Ted's quotes in recent emails to us:
The following PDF documents require an Acrobat Reader (it is free):
NORTHWEST AFRICA 2975: AN EVOLVED BASALTIC SHERGOTTITE WITH VESICULAR GLASS POCKETS AND TRAPPED MELT INCLUSIONS. J.H. Wittke, T. E. Bunch, A. J. Irving, M. Farmer, J. Strope, Dept. of Gelogy, Northern Arizona University, Flagstaff, AZ 86011, Dept. of Earth & Space Sciences, University of Washington, Seattle, WA 98195. Abstract submitted for presentation as poster at the LPSC in Houston in March, 2006.
The Mars Meteorite Compendium - Compiled by Charles Meyer for Astromaterials Research and Exploration Science (ARES)
70.1 gram individual before cutting:
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49.7 gram main mass endcut:
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Cut face measures 44mm by 36mm. Endcut is 26mm deep at widest point.
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