NWA 11757 UREILITE

Northwest Africa 13360 (NWA 13360)

Northwest Africa

Purchased: 2020 Jan

Classification: Martian meteorite (Shergottite)

History: Purchased in January 2020 by Noreddine Azelmat from a moroccan dealer.

Physical characteristics: Single stone lacking fusion crust. A slice of the interior reveals a relatively coarse-grained rock containing brown olivines and gray-green pyroxenes.

Petrography: (Daniel Sheikh, FSU) Sample exhibits a predominantly poikilitic texture (grain size Av. 750±100 µm, up to 2.5 mm) composed of compositionally zoned low-Ca pyroxene oikocrysts enclosing sub-angular olivine chadacrysts. Also present include compositionally zoned, tabular, irregular grains of pigeonite and augite, as well as laths of maskelynite. Accessory phases include chromite (some Ti-rich), ilmenite, pyrrhotite, merrillite, pentlandite, and Si-Al-rich glass. Sample contains minor carbonate weathering veins.

Geochemistry: Olivine (Fa_35.0±1.8, range Fa_30.4-39.4, FeO/MnO=48±5, n=75), low-Ca pyroxene (Fs_21.3±0.4Wo_4.1±0.6, range Fs_20.5-22.5 Wo_3.5-5.2, FeO/MnO=30±3, n=30), pigeonite (Fs_25.5±3.2Wo_9.2±2.8, range Fs_21.8-30.1Wo_6.1-15.4, FeO/MnO=30±3, n=31), subcalcic augite (Fs_16.4±0.8Wo_31.9±2.1, range Fs_15.2-17.7Wo_27.9-34.9, FeO/MnO=22±2, n=20), maskelynite (An_54.2±1.4Or_1.4±0.2, range An_51.3-56.3Or_1.1-1.7, n=20).

Classification: Shergottite (poikilitic). Silicate chemistry, the presence of maskelynite, and FeO/MnO ratios of pyroxenes provide support for classification as shergottite. Predominant poikilitic texture argues for classification as poikilitic shergottite.