Northwest Africa 2420 (NWA 2420)

(Northwest Africa)

Purchased: Jan 2017

Classification: Lunar meteorite

History: The meteorite was exported from Morocco to Tucson where it was purchased by N. Gessler.

Physical characteristics: Dark grey matrix with lighter gray to white clasts up to 7 mm.

Petrography: Overall, the sample consists preponderantly of plagioclase, although mafic silicates are comparably abundant in some clasts. The texture is a fine-grained and obviously polymict breccia, but hard to precisely classify. The groundmass is especially fine grained and locally vesicular. But most of the rock consists of diverse lithic and mineral clasts that survived the breccia-forming process. The clasts include earlier-generation impact melt products akin to "crystalline lunar spherules". Glass (i.e., clearly regolithic) spheroids are not found. Several patches of brown, swirly, vesicular glass suggest a possible minor component of regolithic derivation, but the brown color is less diagnostic in a meteoritic find than it would be an Apollo breccia.

Geochemistry: Low-Ca pyroxene (11 analyses) is compositionally diverse, e.g., Fs₃₀Wo₁₁, Fs₅₁Wo₉, with average FeO/MnO = 55.9; while 2 augite analyses are Fs₂₀Wo₄₁ and Fs₂₆Wo_40. Plagioclase (9 analyses) is An_95.4-96.8, average An_96.1. The bulk composition, determined by INAA and fused-bead EPMA applied to 2 chips totaling 670 mg, is uncommonly aluminous (31 wt% Al₂O₃) even for a lunar highland breccia, and also ferroan with bulk Mg/(Mg+Fe) = 57 mol%. For the middle REE Sm, as a representative incompatible element, the sample has 0.9 µg/g, and for the arch-incompatible Th, 0.2 µg/g.

Classification: Lunar highland polymict breccia

Specimens: Main mass with Gessler, type specimen at UCLA.