from The
Meteoritical Bulletin,
no. 93, Meteoritics & Planetary Science 43,
571-632 (2007)
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, 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 (Fs48.9 – 67.5Wo2.2 – 4.3;
FeO/MnO = 56), exsolution lamellae (Fs24.4 – 41.4Wo12.3 – 32.9;
FeO/MnO = 60). Anorthositic norite: orthopyroxene (Fs35.4Wo4.3) and plagioclase
(An96.5). Anorthositic troctolite olivine (Fa28.1; FeO/ MnO = 105), pigeonite
(Fs26.9Wo5.9; 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%, Ni = 290 ppm, Sm = 3.4 ppm,
Th = 1.5 ppm, Ir = 12 ppb,.
Classification: Achondrite (lunar, feldspathic breccia).
Type specimen: A total
of 20.3 g is on deposit at NAU. The main mass holder is anonymous.
|
