Lunar Meteorite: Northwest Africa 15963

from The Meteoritical Bulletin, No. 112

Northwest Africa 15963 (NWA 15963)

(Northwestern Africa)
Purchased: 20xx
Mass: xx g (1 piece)

Lunar meteorite (anorthosite)

Physical Characteristics: Acquired as two stones, 50 and 6 g, both roughly egg shaped. We have studied thin sections from both stones. The surface lacks fusion crust, and has a smooth appearance as if ablated by sand blasting. The color is mostly medium brown, but with a sprinkling of diverse dark brown to light-gray clasts up to 1 cm across.

Petrography: (P. Warren, UCLA) The rock is a lunar highland impact melt breccia, roughly 92 vol% plagioclase, 8 vol% mafic silicates, mostly pyroxene. The groundmass is extremely fine-grained. Clasts are up to 10 mm but mostly much smaller and about equally as fine-grained as the groundmass. As evidence of very hot, impact-melt style petrogenesis, most of the larger mafic silicates are isolated relict pyroxenes with distinctive reaction rims (very fine grained and subophitic, and incongruously basaltic, subequal pyroxene + plagioclase, in modal composition). Olivine, if present, is far subordinate to pyroxene. Minor phases include kamacite and Saharan Ba-sulfate and Ca-carbonate.

Geochemistry: Mineral compositions and geochemistry: Six kamacite analyses cluster at 92.1 wt% Fe, 7.0 wt% Ni, 0.50 wt% Co; confirming the stone is a meteorite. Plagioclase (40 analyses) is An_91.0±6.8, or An_93.7±4.4 if 8 reaction-rim points are excluded. Pyroxene (46 analyses) is compositionally diverse, with the field on the pyroxene quadrilateral roughly defined by the following: Fs₃₅Wo₃, Fs₂₇Wo₁₂, Fs₃₃Wo₄₁ and Fs₈₉Wo₂₁ (the most extremely ferroan compositions are reaction-rim materials). Pyroxene FeO/MnO (wt.) averages 55±11. Bulk composition results from fused-bead EPMA include SiO₂ = 45.0 wt%, Al₂O₃ = 32.0 wt%, CaO = 17.4 wt%, FeO = 2.3 wt%, MgO = 2.18 wt%, FeO/MnO approx. 59, and Mg# = 63 mol%.

Classification: Lunar anorthositic impact melt breccia.

Specimens: 17 g at UCLA, main mass (39 g) with Gessler.

Randy Says…

I have not studied Northwest Africa 15963.

More Information

Meteoritical Bulletin Database

NWA 15963