Northwest Africa 13257 (NWA 13257)

(Northwest Africa)

Purchased: 2018

Classification: Martian meteorite (Shergottite)

History: Purchased in 2018 by Daoud Wabich from a meteorite dealer in Algeria.

Physical characteristics: Multiple stones with weathered fusion crust.

Petrography: (D. Sheikh, FSU) Sample is a diabase having a predominantly subophitic texture composed of zoned, tabular and prismatic (sometimes twinned) chadacrysts of subcalcic augite and pigeonite (Av. 600±50 µm, up to 1 mm, 58 vol%) contained within larger oikocrysts of maskelynite (Av. 800±50µm, up to 2mm, 42 vol%). Accessory phases include titanomagnetite (some Cr rich), silica, Si-Al-K-Na rich glass, merrillite, chlorapatite, and pyrrhotite. Sample contains minor carbonate weathering veins.

Geochemistry: Subcalcic augite (Fs_34.2±8.7 Wo_30.9±2.1, range Fs_20.4-46.2Wo_26.5-35.7, FeO/MnO=34±5, n=30) pigeonite (Fs_51.3±5.7Wo_15.0±3.1, range Fs_39.4-61.9Wo_10.7-22.8, FeO/MnO=35±4, n=30) maskelynite (An_47.4±6.9Or_2.4±1.2, range An_34.7-58.7Or_0.5-4.8, n=26).

Classification: Martian (shergottite, diabasic) Silicate chemistry, the presence of maskelynite, FeO/MnO ratios of pyroxenes, and magnetic susceptibility provide support for classification as shergottite. Average grain sizes of pyroxenes and maskelynite larger than that of basaltic shergottites, but smaller than gabbroic shergottites, hence diabasic.

Specimens: 21.3 grams at UCLA; main mass with Daoud Wabich.