Meteorite MIL03346, recovered from Antarctica, is a nakhlite: an augite clinopyroxenite inferred to have originated from Mars' surface. MIL03346 contains ~70% augite and 3% olivine in a fine-grained mesostasis of basaltic glass, olivine, titanomagnetite, and pyrrhotite. Part of the olivine is altered to fine-grained ferric clays and oxides: iddingsite as described in other nakhlites. Chemical compositions of augite and olivine (FeO/MnO and Fe/Mg) are nearly identical to those of other nakhlites and are consistent with a Martian origin. The augite contains significant Fe3+: ~24% of total iron by M¿ssbauer spectroscopy and ~13% by elemental analyses and crystal chemistry. This proportion of Fe3+ in augite is consistent with high-temperature equilibration near the QFM oxygen buffer. Thermal emission spectra are similar to those of other nakhlites. Visible to mid-IR spectra of MIL03346 show the same absorption features as do other nakhlites but at distinctly lower reflectances (which likely represent Fe3+ in augite and magnetite). MIL03346 appears to contain the most Fe3+ of any Martian meteorite studied to date and to have come from the most oxidizing magmatic environment yet reported.