Northwest Africa 13531 (NWA 13531)

(Northwest Africa)

Purchased: 2017 Mar

Classification: Lunar meteorite (feldspathic breccia)

History: Writeup history: History: Roger Kilchenmann obtained this meteorite in March 2017 from Noreddine Azelmat of Morocco as part of an online trade for a lot of NWA meteorites.

Physical characteristics: Exterior covered with weathering rind and remnant fusion crust. Cut face reveals predominantly light toned interior with darker veins and pockets, with small (<=1 mm) white clasts.

Petrography: (M. Hutson, A. Ruzicka, Cascadia): Two lithologies are visible in thin section; both are breccias consisting of feldspathic clasts set in a finer-grained matrix dominated by pigeonite and plagioclase. The two lithologies differ in size of feldspathic clasts (up to 2 mm across in lithology 1, up to 0.7 mm across in lithology 2) and matrix texture (blocky plagioclase grains up to 0.1-0.2 mm across in lithology 1, lath-like plagioclase grains <0.1 mm long in lithology 2). An ovoid shaped patch of clast-laden brownish glass about 1 mm in length and thin glassy melt veins occur along the boundary between the two lithologies. Mineral phases present include plagioclase feldspar, pigeonite, augite, olivine, Cl-containing phosphate, ilmenite, Ti-rich spinel, chromite, troilite, and rare tiny (<= 10 μm across) FeNi metal.

Geochemistry: Mineral compositions and geochemistry: (M. Hutson, A. Ruzicka, Cascadia; K. Ziegler, UNM): Oxygen isotopes on acid treated samples in per mil, relative to V-SMOW linearized values): δ¹⁷O’ = 3.083±0.031, δ¹⁸O’ = 5.933±.052, Δ¹⁷O’ = -0.050±.005 (N=3). Plagioclase compositions of clasts are variable, but the range of compositions in the two lithologies overlap. Lithology 1 clasts: An_87-96Or_0.7-1.5 (N=18, 2 clasts); Lithology 2 clasts: An_89-95Or_0.7-1.1 (N=21, 3 clasts). Matrix plagioclase for the two lithologies is also similar. Lithology 1 matrix: An_91.3±2.3Or_0.9±0.6 (N=23); Lithology 2 matrix: An_92.7±2.2Or_0.9±0.9 (N=27). Matrix pigeonite (Wo_5-20) and olivine grains are more magnesian in lithology 1 than in lithology 2. Lithology 1 matrix pigeonite: Fs_29.9±3.1, Mg# = 67.9±3.2 (N=17); Lithology 2 matrix pigeonite: Fs_31.7±1.9, Mg# = 64.2±1.1 (N=13); Lithology 1 matrix olivine: Fa_39.8±2.2, Mg# = 60.2±2.1 (N=11); Lithology 2 matrix olivine: Fa_43.4±0.9, Mg# = 56.5±0.9 (N=15).

Classification: Lunar feldspathic breccia based on texture and mineralogy.

Specimens: Cascadia holds 7.9 g in pieces, as well as a polished thin section and butt.