Infrared spectra and crystal chemistry of scapolites - Implications for Martian mineralogy

Near-IR and mid-IR spectra of 27 scapolites with a wide range of compositions were compared to the features of the 2.35-micron band absorption system that was recently discovered in reflectance spectra of Mars. Results suggest that the 2.36-micron features are due to the presence of small amounts (about 0.5 wt pct each) of HCO3(-) and HSO4(-) in the anion sites of a scapolite. Five of the scapolites (including two meionite and three mizzonite samples) showed absorption features unique to HCO3(-) and HSO4(-). It was determined that the features of the 2.36-micron-centered system are produced by a disordered anion site occupancy and that the band intensity also depends on the HCO3(-)/HSO4(-) ratio. It was found (Clark et al., 1990) that HCO3(-) and HSO4(-) bearing minerals other than scapolites do not exhibit spectral features of the scapolite.