Northwest Africa 4819

Northwest Africa

Find: 2007

Achondrite (lunar, feldspathic breccia)

History and Physical characteristics: A single 234 g crusted stone was purchased in Rissani, Morocco in 2007. The crust is fresh with dark gray to black crusted areas and vermillion to light brown in abraded to weathered areas; some areas show melt bubbles and flow. A network of thin fractures is filled with weathering products.

Petrography: (T. Bunch and J. Wittke, NAU; A. Irving, UWS) This stone is very dark, well indurated, and is fine-grained with few clasts that exceed one mm in diameter. No evidence of flow orientation was observed. NWA 4819 is a regolith breccia and has two unusual characteristics for a lunar sample: (1) a relatively large amount of homogeneously distributed fine-grained metallic nickel-iron (2 wt%) and troilite (1.5 wt%) and (2) a large population of pyroxene fragments. Most lithic clasts follow the ferroan anorthositic trend and include anorthosites, fine-grained anorthositic norites, gabbros, and troctolites, in addition to shock melt clast, K-rich glass, and spherules. No intact basaltic clasts were observed and all clasts are crushed to some extent.

Mineral compositions and Geochemistry: Host orthopyroxene (Fs_48.9-67.5Wo_2.2-4.3; FeO/MnO = 56), exsolution lamellae (Fs_24.4-41.4Wo_12.3-32.9; FeO/MnO = 60). Anorthositic norite: orthopyroxene (Fs_35.4Wo_4.3) and plagioclase (An_96.5). Anorthositic troctolite olivine (Fa_28.1; FeO/MnO = 105), pigeonite (Fs_26.9Wo_5.9; FeO/MnO = 54), plagioclase (An₉₇) and chromite (cr# = 80). Kamacite (mean Ni = 6.2, Co = 0.77 (both wt%) and taenite (Ni = 8.2- 23.6 wt%). Bulk composition: (R. Korotev, WUSL): FeO = 7.0% wt%, Ni = 290 ppm, Sm = 3.4 ppm, Th = 1.5 ppm, Ir = 12 ppb.

Classification: Achondrite (lunar, feldspathic breccia).

Type specimens: A total of 20.3 g is on deposit at NAU. The main mass holder is anonymous.

Submitted by: T. Bunch, NAU.