REFLECTANCE SPECTRA OF HYDRATED SILICA-RICH MATERIALS: SENSITIVITY TO THE FORM OF WATER AND IMPLICATIONS FOR MARS

Hydrated silica-rich materials have recently been discovered on the surface of Mars by the Mars Exploration Rover (MER) Spirit at Gusev Crater and by the Compact Reconnaisance Imaging Spectrometer for Mars (CRISM) in the Valles Marineris region. Having been interpreted as hydrothermal deposits and aqueous alteration products, these materials have important implications for the history of water on the Martian surface. Spectral detections of these materials in visible to near infrared (Vis-NIR) wavelengths have been based on a water feature in the 934 to 1009 nm region seen with Spirit’s Pancam instrument, and on Si–OH absorption features in the 2.21 to 2.26 micron range seen with CRISM. Our work aims to determine how the spectral reflectance properties of silica-rich materials in these wavelength regions vary as a function of environmental conditions and formation. Here we present laboratory reflectance spectra we have acquired of a diverse suite of silica-rich materials (opal, sinter, silica gel, tektites, silica-coated basalt, chert, etc.) under a range of temperature, pressure, humidity, and grain size conditions. We find that the water content and form of water/hydroxyl present in silica-rich materials can have significant effects on their Vis-NIR spectra. The results of this study will aid in the interpretation of the form and content of water in silica detections on Mars.