NWA 12342 Eucrite Melt Breccia
Northwest Africa 12342 (NWA 12342)
Purchased: 2018 Aug
Classification: HED achondrite (Eucrite, melt breccia)
Petrography: (K. Metzler, IfP) Subrounded eucritic lithic clasts (up to 2 cm) with ophitic to subophitic textures and mineral fragments (pyroxene, plagioclase, silica polymorph) embedded in a vesicular crystallized melt. The modal amount of melt is 30-50 vol%. The latter shows a fan-spherulitic texture consisting of skeletal pyroxene and plagioclase crystals with sizes up to 100 µm. Vesicles can reach sizes of ~400 µm. Many lithic clasts are surrounded by a thin dark layer of a more fine-grained crystallized melt. Most pyroxene fragments show shock-deformed exsolution lamellae. Accessories are silica polymorph, ilmenite, Cr-spinel, and troilite.
Geochemistry: Mineral compositions and geochemistry: Lithic clasts: Low-Ca pyroxene Fs59.8±2.0Wo3.5±1.4 (Fs56.1-62.8Wo1.8-6.2); mean Fe/Mn (at.): 33; n=14. Ca-pyroxene Fs26.7±0.4 Wo43.2±0.4 (Fs25.9-27.3Wo42.7-44.1; n=12). Plagioclase An88.9±1.1Or0.4±0.3 (An87.9-90.6Or0-0.8); n=8.