from The Meteoritical Bulletin, No. 110
Northwest Africa 13638 (NWA 13638)
Classification: Lunar meteorite (feldspathic breccia)
Physical characteristics: Single stone, weathered exterior without fusion crust; Cut surfaces reveal >25 vol% angular rock and mineral clasts in a black matrix.
Petrography: (Y. Liu, JPL) Polished thick sections were observed using EMP and SEM. Rock clasts include angular fragments of basalts, anorthosite, and breccias. Graphic granite fragments are present, that contain a silica phase, orthoclase, zirconolite, tranquillityite, and apatite. Mineral fragments are mostly pyroxene and plagioclase with minor amounts of olivine and trace amounts of silica phases and apatite. Matrix is glassy and black. Terrestrial weathering in the form of carbonate in fractures, but no alteration rims on metals and sulfides.
Geochemistry: Mineral compositions (Y. Liu, JPL): Olivine, 55.4 ±24.0 (Fa96-33, molar Fe/Mn 94±16, n=9); Low-Ca pyroxene, Fs42.0±5.7Wo2.5±0.5 (Fs38-46Wo2-3, Fe/Mn 47±1, n =2); Pigeonite, Fs37.1±10.5Wo11.3±3.1 (Fs28-69Wo5-15, Fe/Mn=62.5±5.5, n=16), High-Ca pyroxene, Fs43.0±15.8Wo26.7±7.5 (Fs20-73Wo16-37, Fe/Mn=65.6±8.6, n = 37); Plagioclase, An91.8±4.5Ab7.5±4.2 (An83-99Ab1-16, n =23).
Classification: Achondrite (Lunar polymict melt breccia)
Specimens: 20 g at UCLA (A Rubin). The remainder is held by MtMorgan at Mile High Meteorites.
I have not studied NWA 13638.
Meteoritical Bulletin Database
Liu Y., Ma C., and Morgan M. (2021) Preliminary results of a new lunar impact-melt breccia meteorite Northwestern (NWA) 13638. 52nd Lunar and Planetary Science Conference, abstract no. 1501.