Raman spectroscopy as a method for mineral identification on lunar robotic exploration missions

The sharp, nonoverlapping Raman bands for plagioclase, pyroxene, and olivine would be advantageous for on-surface, active mineralogical nalysis of lunar materials. A robust, light-weight, low-power, over-based Raman spectrometer with a laser exciting source, entirely transmission-mode holographic optics, and a charge-coupled device (CCD) detector could fit within a <20 cm cube. A sensor head on the end of an optical fiber bundle that carried the laser beam and returned the scattered radiation could be placed against surfaces at any desired angle by a deployment mechanism; otherwise, the instrument would need no moving parts. A modem micro-Raman spectrometer with its beam broadened (to .expand the spot o 50-gm diameter) and set for low resolution (7 cm '• in the 100-1400 cm '• region relative to 514.5-nm excitation), was used to simulate the spectra nticipated from a rover instrument. We present spectra for lunar mineral grains, <1 mm soil fines, breccia fragments, and glasses. From frequencies ofolivine peaks, we derived sufficiently precise forsteritc ontents to correlate the analyzed grains to known rock types and we obtained appropriate forsteritc ontents from weak signals above background in soil fines and breccias. Peak positions of pyroxenes were sufficiently well determined todistinguish among orthorhombic, monoclinic, and triclinic (pyroxenoid) structures; additional information can be obtained from pyroxene spectra, but requires further laboratory calibration. Plagioclase provided sharp peaks in soil fines and most breccias even when the glass content was high.