The successful landing of the Mars Science Laboratory Curiosity rover in Gale Crater, Mars, presents a rare opportunity for validation of a spectral index developed for determining olivine chemistry from orbital midinfrared remote-sensing data. Here, a spectral index is developed using laboratory emissivity data of 13 synthetic Mg-Fe olivines. Utilizing this spectral index, a prediction of olivine composition (~Fo55 ± 5) is made from orbital data for a NE-SW trending dune field near the Curiosity rover. This dune field will be crossed during the mission as the rover travels toward a ~5 km-high sediment stack (Mount Sharp) that contains orbitally detected clays and sulfates. Curiosity can use its instrument suite (ChemMin, Alpha Particle X-ray Spectrometer, ChemCam) when it reaches the dunes to verify or refute the olivine-chemistry prediction presented here. The ability to validate the developed spectral index using the rover's ground-truth instruments will strengthen olivine-chemistry mapping across the Martian surface using this spectral index.