[meteorite-list] Met Bulletin Update - New NWA Shergottite

[Galactic Stone & Ironworks]

Hi Bulletin Watchers,

One new approval - a shergottite, NWA 7755.

Link - http://www.lpi.usra.edu/meteor/metbull.php?code=57166

Text -

Northwest Africa 7755 (NWA 7755)

Morocco

Purchased: 2013

Classification: Martian meteorite (Shergottite)

History: Purchased by Matt Morgan and Lee Morgan in 2013 from a
Moroccan meteorite dealer.

Physical characteristics: Single stone with black glassy fusion crust,
with some light-colored desert sediment coating. A saw cut reveals
poikilitic texture.

Petrography: (C. Agee, UNM) Microprobe examination of a polished epoxy
mount shows ~45% olivine, ~35% pyroxene, ~20% maskelynite, ubiquitous
Cr-Ti-Fe oxides. Pyroxenes and olivines are highly equilibrated, with
no zonation in BSE images, heavily shocked, grain size ranges from
200-1000 μm.

Geochemistry: (C. Agee and L. Burkemper, UNM) EMPA. Olivine
Fa38.5±0.8, Fe/Mn=48±2, n=38; pigeonite Fs29.4±1.5Wo10.4±2.4,
Fe/Mn=28±1, n=33; augite Fs18.2±1.2Wo34.2±2.4, Fe/Mn=26±2, n=7;
maskelynite Or2.3±0.3Ab46.0±2.3An51.6±2.4 N=20. Oxygen Isotopes, laser
fluorination (K. Ziegler, UNM), analyses on 3 acid-washed aliquots,
1.5, 1.4, 1.0 mg, gave values δ17O=2.988, 2.882, 2.735; δ18O=5.188,
4.886, 4.696; Δ17O=0.249, 0.302, 0.256 (linearized, all permil).

Classification: Achondrite (Martian, shergottite), petrologically
equilibrated ultramafic rock, poikilitic shergottite group, with
relatively high modal maskelynite, but lacking pyroxene
crystallization trends seen in olivine-phyric basaltic shergottites.
No known pairings, but pyroxene and olivine compositions are similar
to RBT 04262.

Specimens: 6 g including microprobe mount on deposit UNM, Matt Morgan
holds the main mass.

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