Northwest Africa 12320 (NWA 12320)

Mauritania

Purchased: 2018 Apr

Classification: Angrite

History: Two large, dark gray stones (2379 g and 1946 g) plus several smaller stones were found together at an unspecified site in Mauritania, and subsequently purchased by Darryl Pitt in April-July 2018 from a dealer in Nouakchott, Mauritania. An additional 14.2 g of the same material (confirmed by electron microprobe analyses) was purchased by Ben Hoefnagels in October 2018 from a Moroccan dealer.

Petrography: (A. Irving and S. Kuehner, UWS) Diabasic texture (grainsize 0.3-0.5 mm) with sparse vesicles containing partial interior coatings of secondary calcite and barite. Major minerals are zoned calcic olivine (with kirschsteinite rims), zoned Al-Ti-augite and anorthite (with slightly more sodic rims), together with accessory titanomagnetite, troilite and silicoapatite. Sparse xenocrysts of magnesian olivine with more ferroan reaction rims are present.

Geochemistry: Olivine (Fa_39.6-79.7Ln1.7-14.8, FeO/MnO = 72-96, N = 5), clinopyroxene (Fs_20.5-45.9Wo_51.6-52.8, FeO/MnO = 68-143, TiO₂ = 1.5-4.3 wt.%, Al₂O₃ = 6.9-7.8 wt.%, N = 4), kirschsteinite (Fa_57.9-63.3Ln36.7-34.3, FeO/MnO = 68-75, N = 2), olivine xenocryst (core Fa_13.8Ln0.6; rim Fa_35.2Ln1.3; FeO/MnO = 85-103; N = 2), anorthite (core An_99.7Ab_0.2Or_0.0; rim An_96.6Ab_3.3Or_0.1; N = 2). Oxygen isotopes (K. Ziegler, UNM) Analyses of acid-washed subsamples by laser fluorination gave, respectively δ¹⁷O 2.268, 2.281, 2.339; δ¹⁸O 4.416, 4.407, 4.545; Δ¹⁷O -0.063, -0.046, -0.060 per mil.

Classification: Angrite (diabasic).

Specimens: 20.6 g including one polished thin section at UWB; remainder with DPitt, except for 14.2 g with Mr. B. Hoefnagels.