A second Martian meteorite has been identified that is composed primarily of heavily shocked dunite, Northwest Africa (NWA) 2737. This meteorite has several similarities to the Chassigny dunite cumulate, but the olivine is more Mg-rich and, most notably, is very dark and visually brown. Carefully coordinated analyses of NWA 2737 whole rock and olivine separates were undertaken using visible and near-infrared reflectance, mid-infrared emission and reflectance, and Mössbauer spectroscopic studies of the same samples along with detailed petrography, chemistry, SEM and TEM analyses. Mid-infrared spectra of this sample indicate that the olivine is fully crystalline and that its molecular structure remains intact. The unusual color and spectral properties that extend from the visible through the near-infrared part of the spectrum are shown to be due to nanophase metallic iron particles (npFe⁰) dispersed throughout the olivine during a major shock event on Mars. Although a minor amount of Fe³⁺ is present, it cannot account for the well-documented unusual optical properties of Martian meteorite NWA 2737. Perhaps unique to the Martian environment, this "brown" olivine exhibits spectral properties that can potentially be used to remotely explore the P-T history of surface geology as well as assess surface composition.