Petrographic and Mineral–Chemical Heterogeneity in the Elephant Moraine 90299, EL3 Chondrite

We present new petrographic and mineral–chemical data on the Antarctic EL3 enstatite chondrite Elephant Moraine 90299 (EET 90299), obtained by optical microscopy, scanning electron microscopy with energy-dispersive spectroscopy (SEM-EDS), and electron microprobe analysis (EMPA-WDS). EET 90299 preserves well-defined chondrule textures—barred pyroxene, radial pyroxene, porphyritic olivine–pyroxene (POP), and layered chondrules—together with brecciated clasts, showing substantial preservation of chondrule microstructures. The silicate assemblage is dominated by highly magnesian low-Ca pyroxene (Fs 0.7–2.1 mol%). Rare olivine crystals—average Fa 0.33 mol%—found in a POP chondrule are reported for the first time in EET 90299. Chondrule mesostasis shows compositional variability, from predominantly Na–Al and Si-rich to Ca-Na-Al, documenting chemical heterogeneity at the chondrule scale. A euhedral plagioclase crystal identified outside a chondrule displays heterogeneous Na–Ca distribution. The opaque phases comprise kamacite, schreibersite, alabandite, and troilite showing variable Cr contents (2.84 ± 1.07 wt%). The presence of metal–sulphide–silicate intergrowths (MSSI) whose origin remains ambiguous, indicates highly reduced conditions. Opaque-filled micro-veinlets and a wider opaque-rich vein document localized brittle deformation and concentration/redistribution of opaque phases, without pervasively disturbing the primary chondritic texture. Overall, EET 90299 documents the coexistence of well-preserved unequilibrated textures and localized secondary features, providing new micro-scale insights into EL3 chondrite evolution.